Add an XFAIL regression test for issue 4479, multiline svn:special truncated.

* subversion/tests/cmdline/special_tests.py
  (multiline_special): New test.
  (test_list): Add new test.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1577082 13f79535-47bb-0310-9956-ffa450edef68