build-sys: use wildcard glob in update-man-list again

The idea is that after adding a new man page, make update-man-list
will be used to regenerate part of the makefile. So the data already
present in the makefile cannot be used to do that.

Also, renames filter out generated xml files in make-man-rules.py
itself in order to make Makefile.am a bit simpler, and rename files
to dist_files to better reflect new meaning.