On the 1.7.x branch, merge r1445753 from trunk, resolving conflicts.

* subversion/tests/cmdline/externals_tests.py: Add only the new test
   for issue #3741 (update_dir_external_shallow), not unrelated tests
   which are new on trunk and added during the merge.

 * r1445753
   Fix issue #3741, 'externals not removed when working copy is made shallow'.
   Justification:
     Externals linger after update --set-depth empty, causing unnecessary
     tree conflicts when the working copy is updated back to depth infinity.
     See regression test and also the recipe script attached to issue #3741.
   Votes:
     +1: stsp, rhuijben, breser
     -0: danielsh (merge conflicts)



git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/1.7.x@1485384 13f79535-47bb-0310-9956-ffa450edef68