The documentation generation with doxygen now works when built out of tree,
with srcdir != builddir. xcb.doxygen now gets generated from xcb.doxygen.in,
so that it can use top_builddir and top_srcdir to find source and to output
documentation. Also fill in PROJECT_NUMBER from @VERSION@, now that we have
it readily available via autoconf.
Based on a patch by Vincent Torri. Changes from that patch: add Requires to the .pc.in files based on the <import>s in the extensions, add a .pc.in file for libXCBxtest, change Name and Description fields to match extension names.
Josh Triplett
TORRI Vincent
Jeremy Kolb