(svn r7331) - Codechange: Rename all memory pool macro's and types to "old pool", so the new pool implementation can be committed alongside it.
- Codechange: Rename pool.[ch] to oldpool.[ch].

(svn r6153) -Codechange: DeleteSign removes a sign from the pool
-Codechange: DestroySign is called by DeleteSign to remove all things where a sign depends on.
Last 2 changes to prepare for new pool system. Not pretty now, will be soon.

(svn r6137) -Codechange: some very minor cleanups:
- Start using DeleteXXX for every pool item, not manually doing it
- Use some wrapper to improve logic
- Rewrote some pieces to improve logic

(svn r6055) -Codechange: added GetXXXArraySize, which returns HighestID + 1 (or, will do that).
It isn't the best name, but we couldn't find any better.
This unifies the pool-system even more.

(svn r6054) Change the sign sorter in a similar way as the other sorters: Remember a list of pointers to signs instead of a list of SignIDs - This removes a layer of indirection
Also make the sign list static

(svn r6053) -Codechange: renamed all IsXXXIndex to IsValidXXXID
-Codechange: IsValidXXXID now also checks if XXX is really valid, not if the number is within range
Both changes again in preperation of the new mem-pool system, which requires this.
IsValidXXXID is not a bit less pretty, but that will be cleaned up after the new mem-pool system

(svn r6047) -Codechange: FOR_ALL now _only_ loops valid items, and skips invalid ones
-Codechange: use IsValidXXX where ever possible
Note: both changes to prepare for new pool system, which needs those changes.
For every pool there are 2 ugly lines, which will be removed when done
implementing new pool system.
Based on FS#13 by blathijs, partly implemented.

(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 r2079) -Add: signlist, shows all signs in the map. Clicking on them, and you go
to the sign. Very needed for coop. You can find it under World Map.

(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 r1667) - Feature: Signs are now shown in the color of the player who created them
(Note: The player information is currently not stored in savegames. Upon loading a game the signs will all be gray again)

(svn r1486) -Codechange: moved all 'signs' stuff to signs.c/h and prepared it for
dynamic arrays