modifyrepo.py

I just committed a new tool, modifyrepo.py, to CVS.  This tool is used
to insert arbitrary metadata into a given repository.

Example:
    $ ./modifyrepo.py ~/updateinfo.xml ~/tmprepo/repodata
    Wrote: /home/lmacken/tmprepo/repodata/updateinfo.xml.gz
               type = updateinfo
           location = repodata/updateinfo.xml.gz
           checksum = 8ae77bc9a709bcf9c7f030dae3e9f0842803fcca
          timestamp = 1156361029
      open-checksum = 4a694054c7429332281289c16f83452959f359eb
    Wrote: /home/lmacken/tmprepo/repodata/repomd.xml

This is the code that the Fedora Updates system uses to insert extended
metadata into the repos.  From here, the metadata can be retrieved using
the retrieveMD() method in the YumRepository object, or using the
yum.update_md module when dealing with specific extended update metadata.

With the name 'modifyrepo', this should be able to encompass any future
repository modification code people care to whip up.

Comments/questions/patches welcome :)

luke