Added support for SDL2 compilation in vs2010, vs2012, vs2013.

Changed the build directories for all vs2010, vs2012, vs2013 projects - they are now more consistent (output binaries go into SolutionDir, intermediate files have a fully qualified directory so they don't conflict between builds).

Audited and reduced differences between vs2010, vs2012, vs2013 projects.

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@12224 d7cf8633-e32d-0410-b094-e92efae38249
::stable-branch::merge=59d9acac