swig-py: Add test for parse_fns3 baton reference leak (SVN-4918) * subversion/bindings/swig/python/tests/repository.py (DumpStreamParser.__init__): Hold pool object if it is passed. (DumpStreamParser._close_dumpstream): Release the pool. (SubversionRepositoryTestCase.test_parse_fns3): Add test for parse_fns3 baton reference leak (SVN-4918)