Followup to r27607.
Followup to r27607.

* subversion/include/svn_fs.h
  (svn_fs_change_txn_props): Clarify documentation.

Suggested by: blair

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion