New CVar "in_kbd" to set the layout for the keyboard. SDL 1.2
doesn't offer any way to determine it, and we need this feature
to use the same key for toggling the console independent of the
keyboard layout.
The old "in_nograb" from the Linux backend is still supported.
Use SDL to set video modes, get a GL context and detect the
amount of VRAM.
As with the Linux GLimp implementation, sys_videoRam can be used
in case the SDL detection fails.
