On the fsfs-format7 branch: Unbreak the tests.

* subversion/libsvn_fs_fs/low_level.c
  (svn_fs_fs__write_rep_header): fix test for PLAIN reps

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsfs-format7@1430975 13f79535-47bb-0310-9956-ffa450edef68