Make ctypes-python tests pass regardless of timezone.

SvnDate.as_human_string() calls svn_time_to_human_cstring() which provides the
date as a string in the local timezone.  The test was hardcoded to assume the
local timezone was UTC.  Making an exact match against the string would
essentially require a reimplementation of the C function, so just use a regexp
to match that we're getting something in the right format.

* subversion/bindings/ctypes-python/test/svntypes.py
  (test_as_human_string): Use a regexp to validate the function works.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1482554 13f79535-47bb-0310-9956-ffa450edef68