swpipe: Add Framebuffer management

* It's painfully obvious to me now that we will
need to manage our own framebuffers still in
the latest gallium code.
* GalliumFramebuffer works pretty cleanly as a
class.. we have to remember to lock and unlock
the Framebuffer object however when we access
fBuffer directly. (which needs to occur by design)
* I'm really starting to have problems with the
amount of downcasting Gallium3D does now.

swpipe: Handle post processing

* Introduce textures into local gl context

swpipe: Improve context management

* Ensure all context pointers are in a known state
* Destroy all contexts on shutdown

swpipe: Spell check header guard. No funtional change.

* Thanks Urias :)

softpipe: Initial work on Gallium renderer

* This is still early, but I want to track the
development in tree.
* swpipe will support Gallium softpipe or llvmpipe
(llvm pipe will give improved software rendering
permance when llvm is included at os build time)
* Used Artur Wyszynski's original code as a
road map... however a *lot* has changed.
* Crashes at startup.. not in image yet