Attempt to fix build breakage introduced in r1600096, by updating a swig
definition that is now referenced from a struct.

* subversion/bindings/swig/include/svn_containers.swg
  (apr_hash_t *MERGEINFO): Find global pool like how we handle it in other
    locations.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1600265 13f79535-47bb-0310-9956-ffa450edef68