pbuffers, mode setup, etc.

[Brian Paul]

A few things:

I added code to the fb_egl.c file to support s/w-based pbuffers.  It's 
untested, but should likely work.  The code was simple thanks to the 
new renderbuffer stuff.

The _eglConfigToContextModesRec() function can be used to convert an 
_EGLConfig object to a GLvisual/__GLcontextModes object.  I'm using 
that both for pbuffer and screen creation.

I tried to remove all dependencies on the _EGLConfig->glmode field but 
I haven't removed it yet.  Jon, I think using the new 
adaptor/convertor function is cleaner.  Do you agree?

Finally, the _eglFillInConfigs() routine in eglconfig.c looks a little 
too hardware-centric to me.  I think a better home for it would be a 
new driver utilities file.  Jon, what do you think?

Oh, it looks like the eglQueryDisplayMESA() function got reintroduced. 
  I think we had determined that it wasn't needed a couple weeks ago. 
  I removed it from the last EGL_MESA_screen_surface spec.  Did you 
find a new reason for it, Jon?

-Brian