reworked userdir path selection, now has 4 "tiers":

reworked userdir path selection, now has 4 "tiers":
NOHOME - uses basedir for configs
HOME - uses basedir on Windows, ~/.gamename/ on OSX and Linux
MYGAMES - uses My Games on Windows, ~/.gamename/ on Linux and OSX
SAVEDGAMES - uses Saved Games/gamename/ on Vista+, ~/.gamename/ on Linux
and ~/Library/Application Support/gamename/ on OSX
The tiers are tried in reverse order and any existing one will be used,
new ones will always be the last one.
If gamedirname1 is "id1" then Windows will use NOHOME rather than create
a new userdir when none are found. (but you can still create one or use
-mygames or -savedgames commandline options to make it do so)

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@11085 d7cf8633-e32d-0410-b094-e92efae38249