Replace assertions triggered in svn_dirent_get_absolute() triggered by
$ svn pl -r PREV https://svn.apache.org/repos/asf
$ svn pg Q -r PREV https://svn.apache.org/repos/asf
and
$ tortoiseproc /command:properties /path:https://svn.apache.org/repos/asf
(which tries to obtain the WORKING properties)
with a proper error.

* subversion/libsvn_client/prop_commands.c
  (svn_client_propget5): Don't assert when we encounter a url.
    Avoid second conversion to absolute path.

  (get_remote_props): Don't assert when we encounter a url.

* subversion/tests/cmdline/prop_tests.py
  (wc_propop_on_url): New function.
  (test_list): Add wc_propop_on_url.

Found by: Baybora Aksoy <baksoy{_AT_}collab.net>
          CollabNet QA


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1586255 13f79535-47bb-0310-9956-ffa450edef68