Fix the helper function 'change_rev_prop' to use functions which perform
validation of the property value if 'validate_props' is set. Otherwise,
bypass those checks.

* subversion/libsvn_repos/load-fs-vtable.c
  (change_rev_prop): Do the property validation indeed if 'validate_props' is
    set.

Patch by: Vijayaguru G <vijay{_AT_}collab.net>