To automatically include the standard user documentation build files (omf.make
and xmldocs.make) in your package, set USE_COMMON_DOC_BUILD=yes in autogen.sh
before calling the macros2/autogen.sh script.

When porting applications across to use this feature, ensure that all of the
references to xmldocs.make are to $(top_srcdir)/xmldocs.make in the appropriate
Makefile.am files. Some modules assume that xmldocs.make is in another
directory (like docs/ or something).

