Fix our FSFS format compatibility test.  We must check for general
format version support before complaining about unknown options.

* subversion/libsvn_fs_fs/fs_fs.c
  (check_format): moved upward to be available ...
  (read_format): ... here; check format before trying to
                 interpret the rest.
  (svn_fs_fs__open,
   upgrade_body): update callers

Found by: philip

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1534158 13f79535-47bb-0310-9956-ffa450edef68