Fix edge case in the svn_fs_contents_changed for file nodes with matching
MD5 but different contents in FSFS.  If the nodes have different IDs and
the SHA1s are not known (pre-1.6 format revision), always default to
"different".  This is then identical with the pre-1.9 behavior.

The other backends are not affected.

* subversion/libsvn_fs_fs/fs_fs.c
  (svn_fs_fs__file_text_rep_equal): We must report false negative *equals*
                                    instead of false positive ones.

Found by: julianfoad


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1633232 13f79535-47bb-0310-9956-ffa450edef68