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.

(svn r25780) -Change: [DOS] Put cwsdpmi and exe2coff files in subdirectories.
- Since these are different components, distributed under a different
license, mixing them in the same directory is confusing.

(svn r18706) -Cleanup: remove docs/Manual.txt and docs/OSX_install_instructions.txt, the contents of those are already in readme.txt and they were outdated.
Add docs/obm_format.txt and docs/obs_format.txt to Makefile.bundle
Add several documentation files to the windows installer

(svn r15618) -Cleanup: remove unneeded (empty) scenario directory.
Note: as you might know subversion has the tendency to also remove unversioned files when a directory is removed, so scenarios and heightmaps in that directory will be gone too.

(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 r14262) -Feature [Makefile]: Let Makefile.bundle.in also use the new findversion.sh
script. This enables revision detection for bundles for git and hg checkouts.