Revision 1592724

Follow-up to r3265 (r843339): In 'svn propget --revprop', error out on non-existing properties.

* subversion/svn/propget-cmd.c
  (svn_cl__propget): Handle the (propval == NULL) case.

* subversion/include/svn_client.h
  (svn_client_revprop_get): Document API behaviour on non-existing properties.

* subversion/tests/cmdline/svnadmin_tests.py
  (empty_date): Use exit code to verify lack of property.

* subversion/tests/cmdline/prop_tests.py
  (revprop_change): Same.  'propget' was actually already failing (with
    the expected E200017), but the test was ignoring the exit code.
    (I think the before-this-change code can never fail, since
    re.match('cha-ching', 'cha-ching\n') would return False.)