Remove: DOS support

In 10 years there was no active development on DOS. Although it
turned out to still work, the FPS was very bad. There is little
interest in the current community to look into this.

Further more, we like to switch to c++11 functions for threads,
which are not implemented by DJGPP, the only current compiler
for DOS.

Additionally, DOS is the only platform which does not support
networking. It is the reason we have tons of #ifdefs to support
disabling networking.

By removing DOS support, we can both use c++11 functions for threads,
and remove all the code related to disabling network. Sadly, this
means we have to see DOS go.

Of course, if you feel up for the task, simply revert this commit,
and implement stub c++11 functions for threads and stub functions
for networking. We are more than happy to accept such Pull Request.

Fix 5f8354f3: Non-Windows builds did not get correct git hash

Effect is that gamelog and network revisions indicate a git revision of 0, potentially causing issues.

(svn r25108) -Fix: Pass $LDFLAGS_BUILD to all endian_check compilations.
- In Makefile.{lang,setting}.in the flags were already passed since r24365.

(svn r23817) -Fix [FS#4962]: desync due to different NewGRF version. So reduce the chance that it happens significantly with betas/RCs/nightlies by doing the same as is done for stable releases: check the NewGRF version of server vs client.
Previously this check was not done for nightlies/betas/RCs due to missing versioning information in the source tarballs, but they have that for a while now. So just force the NewGRF version check for all versions, and remove the broken --revision configure option

(svn r16318) -Change: use !! instead of @@ in src/*.in too.
-Change: use @ instead of ~ in configure/Makefiles so Debian's build system(s) can also build RC binaries.

(svn r15027) -Merge: tomatos and bananas left to be, here is NoAI for all to see.
NoAI is an API (a framework) to build your own AIs in. See:
http://wiki.openttd.org/wiki/index.php/AI:Main_Page
With many thanks to:
- glx and Rubidium for their syncing, feedback and hard work
- Yexo for his feedback, patches, and AIs which tested the system very deep
- Morloth for his feedback and patches
- TJIP for hosting a challenge which kept NoAI on track
- All AI authors for testing our AI API, and all other people who helped in one way or another
-Remove: all old AIs and their cheats/hacks

(svn r14272) -Fix [Makefile]: Always pass an explicit delimiter to the "cut" command, in
case there are platforms where tab is not the default.

(svn r14261) -Change [Makefile]: Move the revision detection code from Makefile.src.in to a
new bash script findversion.sh. This commit should have no functional changes.

(svn r8678) [PSP] -Add: added LIBS and CFLAGS needed to compile PSP
-Fix: PSP needs to link with gcc, not with g++ (don't ask)
-Fix: PSP doens't support threads

(svn r8605) -Codechange: [OSX] changed all objective C to objective C++
This will permanently solve the issue where compilation on OSX broke because C++ code was added to some header files

-Note: (important if you develop mac specific code)
taken from http://developer.apple.com/releasenotes/Cocoa/Objective-C++.html
gdb lacks an integrated C++ with Objective-C parser. This means that gdb won't be able to evaluate expressions that contain both C++ and Objective-C constructs.
gdb assumes that the language for ".mm" files is C++.
you can change it to objective C by typing: (gdb) set language objc
Mixing C++ and objective C has some limitation (see link for all of them)

(svn r7759) -Merge: makefile rewrite. This merge features:
- A proper ./configure, so everything needs to be configured only once, not for every make.
- Usage of makedepend when available. This greatly reduces the time needed for generating the dependencies.
- A generator for all project files. There is a single file with sources, which is used to generate Makefiles and the project files for MSVC.
- Proper support for OSX universal binaries.
- Object files for non-MSVC compiles are also placed in separate directories, making is faster to switch between debug and release compiles and it does not touch the directory with the source files.
- Functionality to make a bundle of all needed files for for example a nightly or distribution of a binary with all needed GRFs and language files.

Note: as this merge moves almost all files, it is recommended to make a backup of your working copy before updating your working copy.