Remove some redundant code and use an existing private function instead.
Remove some redundant code and use an existing private function instead.

Patch by: julianfoad
Review by: me

* subversion/libsvn_client/mergeinfo.c
  (svn_client__get_repos_mergeinfo_catalog):
  (logs_for_mergeinfo_rangelist):
   Use svn_mergeinfo__add_prefix_to_catalog rather than replicating its
   effects.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion