On the issue-3220-dev branch, finish the basic algorithmic reworking.

* subversion/libsvn_repos/log.c
  (fs_mergeinfo_changed): Reduce some logic.
  (get_combined_mergeinfo_changes): Use a subpool for temporary
    calculations.  Handle mergeinfo changes that affect paths of
    interest via inheritance alone.  Fix some other pool usage issues.
    Disable some debugging output.


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/issue-3220-dev@872222 13f79535-47bb-0310-9956-ffa450edef68