Fix issue #4329 'automatic merge uses reintegrate type merge if source is
fully synced' and issue #4258 'Automatic merge after subtree merge in
opposite direction'.

* subversion/libsvn_client/merge.c

  (operative_rev_receiver): New svn_log_entry_receiver_t callback.

  (find_last_merged_location): Replace target mergeinfo argument with a
   svn_client__pathrev_t representing the target.  Reimplement using
   svn_client_mergeinfo_log2 to find the youngest revision fully merged from
   source to target and the oldest revision eligible for merging from
   source to target. 

  (find_base_on_source,
   find_base_on_target): Update calls to find_last_merged_location().

* subversion/tests/cmdline/merge_automatic_tests.py

  (subtree_to_and_fro,
   effective_sync_results_in_reintegrate): Remove XFail decorator and
   update comments re failure status.

* subversion/tests/cmdline/merge_reintegrate_tests.py

  (reintegrate_with_subtree_merges): Expand test to cover issue #4329.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1464102 13f79535-47bb-0310-9956-ffa450edef68