fsaa support, borrowing from uhexen2. cvar is vid_multisample, cmdline arg is -fsaa (inconsistent..)

git-svn-id: svn://svn.code.sf.net/p/quakespasm/code/trunk@962 af15c1b1-3010-417e-b628-4374ebc0bcbd
cleanup fsaa patch, from szo. removes sdl version checks because qs requires sdl >= 1.2.10

git-svn-id: svn://svn.code.sf.net/p/quakespasm/code/trunk@963 af15c1b1-3010-417e-b628-4374ebc0bcbd