Add regression test for the property handling via the new mtcc api.

* subversion/libsvn_client/mtcc.c
  (mtcc_op_find): Don't segfault when created is NULL.

* subversion/tests/libsvn_client/mtcc-test.c
  (test_swap): Fix whitespace.
  (test_propset): New test.
  (test_list): Add test_propset.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1550816 13f79535-47bb-0310-9956-ffa450edef68