Improve the performance of "log -g" by avoiding scanning the same set of paths/ranges more than once.
Improve the performance of "log -g" by avoiding scanning the same
set of paths/ranges more than once.

* subversion/libsvn_repos/log.c
  (get_combined_mergeinfo_changes): Don't bother combining two NULL
   mergeinfos.
  (reduce_search, store_search): New.
  (handle_merged_revisions): Add processed parameter.
  (do_logs): Add processed parameter, allocate hash, store processed
   paths/revisions and use to avoid duplicate history scans.
  (svn_repos_get_logs4): Pass NULL.

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