Fix issue 4337, client memory leak in "svn log" for ra_svn.

* subversion/libsvn_ra_svn/client.c
  (ra_svn_log): Use iteration pool in loop.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1458341 13f79535-47bb-0310-9956-ffa450edef68