Start using the 'mtcc' api from svnmucc, removing about 30% of the code from
svnmucc.

* subversion/svnmucc/svnmucc.c
  (operation): Remove struct.
  (change_props,
   drive,
   get_operation,
   build): Remove function.

  (execute): Remove unused argument. Build operation using the mtcc api. Use
    iterpool pattern. Remove log message logic.

  (log_message_baton): New struct.
  (log_message_func): New function.
  (sub_main): Setup svn_client_ctx_t log message handling. Update caller.

* subversion/tests/cmdline/svnmucc_tests.py
  (basic_svnmucc): Expect slightly different error codes for certain error
    conditions.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1550968 13f79535-47bb-0310-9956-ffa450edef68