(svn r3652) Rewrite CmdBuildTunnel in the hope to make it a bit more comprehensible
This implementation is also significantly shorter because it removes many redundant checks

(svn r3564) Several smaller changes:
- Don't treat non-booleans as booleans
- Reduce variable scope
- Bracing
- Use DeMorgan's law to make conditionals easier to read
- if cascade -> switch
- Replace some magic numbers by symbolic names
- Avoid assignments within other statements

(svn r3472) - [PBS] Remove from trunk. Anyone interested can still find it in branch/pbs. This reverts revisions r3158, r3140, r3075, r2977, r2674, r2625, r2621, r2529, r2528, r2525, r2524, r2519, r2517, r2516, r2507, r2499. (in conjunction with Tron)
- The only change is that the nsignalsw.grf file is kept and that existing nightlies with PBS signals get those signals converted to combo-signals.

(svn r3308) BAD
foo.h: int bar;

GOOD
foo.h: extern int bar;
foo.c: int bar;

(svn r3218) -Feature: Multiheaded train engines will now stay in the same train
This means that any user attempt to remove a rear engine will tell the user to move the front engine instead
This fixes the assert when moving multiheaded engines (introduced in r3144)
Note: to make old savegames use this feature, some engines might be turned around in order to link engines in pairs

-Codechange: train subtype is now a bitmask
This allows fast access to info like if it is a wagon or engine and if it is in front and so on
Note: savegame version bump

(svn r3181) -Bracing
-Indentation
-Whitespace
-DeMorgan's Law
-Test with NULL or 0 for non-booleans
-'\0' instead of 0 for chars
-Remove redundantly redundant comments (like DoFoo(); // Do foo)
-Join multiple short lines with a single statement
-Split single lines with multiple statements
-Avoid assignments in if

(svn r2962) - const correctness for all Get* functions and most Draw* functions that don't change their pointer parameters
- change a lot of byte player types to PlayerID
- beautify header files, same "#endif /* filename */" ending

(svn r2948) -Fix: the old AI needs a special flag that triggers all kind of special
abilities you really don't want to know about (free bridges, etc..)
I removed this flag some revisions ago, but the Aircraft part
depends on it, so I re-enabled it again..

(svn r2817) -Codechange: [autoreplace]: moved autoreplace and autorenew to serverside
-This means that one company can only have one setting for renew and replacing
more clients will not fight due to different settings anymore
-This is a needed step in the line to fix autoreplacing dualheaded locomotives
NOTE: savegame revision bump (peter1138 + me in coop)

(svn r2702) -Codechange: Cleaned up the sprite code and replaced many magic numbers
by enums. There remains work in gfx.c to move the "transparency" and
"recolor" bits around to make space for more sprites. However, 2800
additional sprites can now be loaded. There also remains cleanup and
Doxygen work on many of the header files.

(svn r2595) -Codechange: Introduced "IsSteepTileh" to find whether a tile is steep
(i.e. spans two height levels) and use it throughout the code.
-Codechange: Add CanBuildDepotByTileh to find if a tile is suitable to
build a depot on it. Wraps some bitmagic which seems quite unreadable at
first glance

(svn r2516) - Feature: [pbs] Implement path-based-signalling. This allows multiple trains within the same signal block, provided their paths dont intersect. For this the block must have all exit and entry signals be pbs signals. Place these by ctrl-clicking 4 times on a normal signal.
- Feature: [pbs] Implement autoplacement of pbs blocks, when a block has an entry and an exit pbs signal, covert the entire block to pbs. Can be turned off in the patch settings.
- Feature: [pbs] Allow showing of reserved status by making the tracks darker, when the pbs debug level is at least 1.

(svn r2288) - CodeChange: protected the next batch of commands (41 so far, out of 115).
- CodeChange: changed the airport gui airport-type checking. Added function GetValidAirports() that returns bitmasked availibility, is also used for checking.
- CodeChange: to check tree-planting, 2 const arrays have been moved to table/tree_land.h (type and count)
- CodeChange: added IsTownIndex() in following of IsStationIndex(), etc.
- Fix (regression): road tunnels did not work anymore, forgot that their type was 0x200 (documented now)

(svn r2286) - CodeChange: paramcheck the next batch of commands.
- Fix (regression): fix up terraform land where every player can terraform land (towns, map generation), and player can terraform different corners; used for building tunnels

(svn r2285) - Codechange: Fix up some of the missing things from server-checking; namely bridge-type, bridge-length, dragged end-tile (bridge/station), station_spread
- Fix: [ 1197256 ] max station spread patch < 7 does not work. Station spread was not taking into account when not using drag&drop. Fix this up, and add a callback to the settings window to immediately reflect the changes.

(svn r2046) -Codechange: moved all waypoint code to waypoint.c/waypoint.h
-Codechange: rewrote some functions while moving waypoint-stuff
-Add: added support for 64k waypoints
-Fix: made the waypoint struct a bit more logic (no bit-fucking)

(svn r1923) - Fix: [ 1155696 ] Crash with german umlauts in station names. The width was not calculated using unsigned values, so all characters above 128 were "negative"
- Codechange: a more proper check for a null pointer in tunnelbridge_cmd.c should have gone in with the previous commit

(svn r1834) - Fix: NPF does not check the owner of its target, busses try to enter other players' depots. TODO
- Add: asserts to find the v->u.rail.track == 0 problem.
- Add: IsValidDepot(), IsValidTown(), IsValidSign(), IsValidVehicle(), IsValidStation()
- Add: GetTileOwner(), IsTileOwner()
- Codechange: Replaced IsShipDepotTile(), IsTrainDepotTile(), IsRoadDepotTile() by IsTileDepotType().
- Codechange: typedeffed the MAP_OWNERS as Owner. Should be used as variable type.
- Codechange: Replaced a few uint by TileIndex.

(svn r1696) Use GetTileSlope() instead of FindLandscapeHeightByTile() where it is sufficient. FindLandscapeHeightByTile() uses GetTileSlope() internally and adds some more info, which is discarded in these cases.
While touching the code make a bit more clear how GetBridgeHeight() works.

(svn r1560) Introduce SetTileType() and SetTileHeight()
Replace direct references to _map_type_and_height with these

(svn r1386) Move TileIndexDiff to map.h
Move _tileoffs_by_dir to map.[ch] and encapsulate it in TileOffsByDir()

(svn r1337) Use MapMax[XY]() (or MapSize[XY]() if appropriate) instead of TILE_MAX_[XY]
While here replace one erroneous TILE_MAX_X with MapMaxY()

(svn r925) Use sound enums
Also play the correct sound when a toyland road vehicle breaks down

(svn r901) Small step in the process to clean up the DPARAM mess:
- reduce to 2 sizes (*DParam64 for 64bit values, *DParam for the rest)
- use inline functions instead of macros
- add assert()s to check for buffer overruns