Fix issue #4310 "each editor drive gets its own notification during
'svn merge'".

* subversion/libsvn_client/merge.c

  (do_file_merge): Reset the merge_b->notified_merge_begin to false after
   each editor drive.

* subversion/tests/cmdline/merge_tests.py

  (multiple_editor_drive_merge_notifications): Remove XFail decorator and
   tweak comments re failure status.



git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1441566 13f79535-47bb-0310-9956-ffa450edef68