Match visuals for fbconfigs, remove get_dpy_fbc (GH-27)
Restrict matching of Visuals for FBConfigs (GH-27)

Return NULL visual if attributes do not match, otherwise if an application
first creates a Pbuffer with an FBConfig, but then decides to use a Visual
to create a context, it might get a BadMatch error due to different alpha.
Revert "Temporarily pretend that GLX_SGIX_pbuffer is supported (GH-27)"

This reverts commit 1a047f74fb024efdba145dc02332a268b066d694.
Do not try to match the exact MSAA factor

Fixes a regression on Torchlight (engine: OGRE), where it would select an
FBConfig with 2x FSAA, and then demanded a corresponding Visual to create a
window, but ddpy only had 4x and 8x FSAA.

Unfortunately, this Visual-FBConfig bridging is a bit fickle, since primus
should provide Visuals for all FBConfigs suitable for rendering into a window,
but restricting the set of exposed FBConfigs is undesirable, and neither is
virtualizing Visuals.
Update default nVidia path
Stop blaming Gentoo, simplify Ubuntu build instructions
Do not create Pbuffers in advance (GH-27)

Instead, just record the dimensions and create during MakeCurrent, thus
following the route taken for other drawables and sidestepping the issue with
application creating a context with a Visual not 100% corresponding to an
FBConfig used to create the Pbuffer.
Allow glXQueryDrawable before a Pbuffer is made current
Try harder to find a somewhat matching Visual (GH-27, GH-87)
Recreate pbuffers for incompatible contexts (fixes GH-84)
Simplify logic in Visual matching
Stringify config vars before passing them to compiler

Otherwise "linux" in "x86_64-linux-gnu" gets expanded to 1
Always fixup incompatible fbconfigs (fixes GH-91)
Use a separate connection for display threads (fixes GH-89)
Add per-drawable reinit todo marker
Detect resizes in the background display thread
Use only the original Window on ddpy (fixes GH-93)
glXSwapBuffers is a no-op for pixmaps
Use TEXTURE_RECTANGLE instead of (npot) TEXTURE_2D
Use a double-buffered texture on ddpy