dga_check.c: Make sure that the version of the VidMode extension at
runtime is the same version we compiled with, to deal with a structure
change that occurred between VidMode extension versions 1 and 2. If a
version 3 is developed, this will have to be fixed again.
int. Cleaned up prototypes to not include variable names.
dga_check.c: Fix bug in DGA detection that lead to segfault.
in_x11.c: Better DGA input support for X targets; The -nodga parameter is
gone, it is now the in_dga Cvar, which is dependant on the _windowed_mouse
Cvar. in_dga is archived.