On the 'move-tracking-2' branch: A follow-up fix after r1626023.

* subversion/libsvn_ra_local/ra_plugin.c
  (fetch_func): Adjust to use a stringbuf for file content.

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/move-tracking-2@1626169 13f79535-47bb-0310-9956-ffa450edef68