Fix a potential pool usage issue.

* subversion/libsvn_fs_fs/fs_fs.c
  (svn_fs_fs__create): All members of FS should be allocated in FS->POOL.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1606551 13f79535-47bb-0310-9956-ffa450edef68