bugfix for bug #6994

[Stefan Dösinger]

Am Sonntag, 23. Dezember 2007 01:43:17 schrieb Alexei Slepov:
> Subject:
>
> We can't use ordinary backbuffer to render textures, which size is more
> than
> size of the screen. To render bigger texture we must use pbuffer.
You can't just set the setting to PBUFFER, you at least have to check if 
pbuffers are supported.

The proper fix is IMHO to fix the problems fbos suffer from and default to fbo 
offscreen rendering