This fixes:
- Mouse grab being lost after alt-enter goes windowed in the SDL driver.
- Joystick ceasing to function on vid_restart in the SDL driver.
- Audio failing to work after after snd_restart in the SDL driver.
- Probably other things.
it'd make it easier on people packaging up quake3 if we could set system paths
for the baseq3 dir and if the makefile would respect things like CC/CXX from the
build env