Make 'svn --version' show available authentication credential caches.

* subversion/svn/help-cmd.c
  (svn_cl__help): Append auth creds storage providers to the version
   footer shown in --version output.

* subversion/tests/cmdline/getopt_tests.py
  (del_lines_res): Add patterns to delete auth-cache related lines
   from --version output.
   
* subversion/tests/cmdline/getopt_tests_data/svn--version--verbose_stdout,
  subversion/tests/cmdline/getopt_tests_data/svn--version_stdout,
   Adjust expected output.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1572106 13f79535-47bb-0310-9956-ffa450edef68