On the authzperf branch: Provide a test for svn_stringbuf_replace_all.

* subversion/tests/libsvn_subr/string-test.c
  (test_stringbuf_replace_all): New test.
  (test_funcs): Register new test.


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/authzperf@1617144 13f79535-47bb-0310-9956-ffa450edef68