Open requested to merge ajax/libglvnd:drop-query-context-info-ext-fallback into master
GLX_EXT_libglvnd requires GLX 1.3, we can assume GLXQueryContext works.
This is somewhat petty. I'm mostly doing this because I'd like to see glvnd only use xcb internally, and xcb's API around vendor-private requests is gross. This is the only non-core-GLX request we emit, so.