Fix a regression in svn_fs_props_changed: it should always report
path@root to be equal to path@root - even for txn roots.

Only FSFS and FSX backends are affected as their property reps are
indistinguishable within a transaction.

* subversion/include/svn_fs.h
  (svn_fs_props_changed): Explain that old releases had a problem
                          with prop lists in FSFS txns.

* subversion/libsvn_fs_fs/fs_fs.c
  (svn_fs_fs__file_text_rep_equal,
   svn_fs_fs__prop_rep_equal): Representation is of the same node
                               always match.

* subversion/libsvn_fs_x/fs_x.c
  (svn_fs_x__prop_rep_equal): Same.

Found by: breser


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1573071 13f79535-47bb-0310-9956-ffa450edef68