Following up on r1550758, add an initial testcase for the svn_client_mtcc
api and fix the first few issues found by running this test.

* build.conf
  (mtcc-test): New test.

* subversion/libsvn_client/mtcc.c
  (mtcc_op_find): Calculate basename correctly. Set output argument.
  (svn_client_mtcc_create): Allocate enough memory.

* subversion/tests/libsvn_client/mtcc-test.c
  New file.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1550765 13f79535-47bb-0310-9956-ffa450edef68