This will be used to handle the corner case when a drawable XID is
passed into the API library which belongs to an X window or otherwise
has never been seen before by the process, by providing a way to lookup
which screen the corresponding drawable belongs. This still is racey
since we can't guarantee a different process won't free the XID and
cause it to be recycled as a handle for a different resource after the
lookup, but better than not being able to figure out the mapping at all.
This extension also solves the less-difficult problem of mapping a
screen to a vendor name (though it may make more sense to at some point
directly map drawables to a vendor to better support render-offload
scenarios).
Move the GLdispatch header file to its own directory in src/GLdispatch,
and build a real DSO that GLX will depend on. In GLdispatch.c, add stub
functions which will later be fleshed out.
This is a wrapper library around libpthread which implements
single-threaded fallbacks in case the API library is loaded in an
application which does not link against pthreads.
