ranges can be used efficiently. move the auto-allocated builtins to
0x10000000-0x7fffffff. should be more than enough :)
use static builtin tables ("nul" terminated) instead of a series of
function calls to add builtins to a vm. should be more memory efficient.
cache the value.
don't call Qopen directly in the engine. instead call QFS_Open (generic) or
QFS_WOpen (write only, zip flag).
rework QFS_NextFilename to use a dstring (avoiding a potential buffer
overflow), support 10000 files and work from the top-level fs_userpath
directory. adjust QFS_WriteFile and QFS_WriteBuffers etc to suit.
make sw32 screenshots actually get written.
hopefully everything gets written to the right places :)
