Reduce memory usage a bit when retrieving revision properties. This
mostly affects svnsync's per revision handling.

* subversion/libsvn_ra_serf/serf.c
  (serf__rev_proplist): Introduce dual pools.
  (svn_ra_serf__rev_proplist,
   svn_ra_serf__rev_prop): Use subpool as callers are expected to pass a
     result pool.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1557689 13f79535-47bb-0310-9956-ffa450edef68
* subversion/libsvn_ra_serf/update.c
  (process_pending): Following up on r1557687, remove unused variable.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1557690 13f79535-47bb-0310-9956-ffa450edef68