Improved documentation for XFail.__init__.
Improved documentation for XFail.__init__.

Suggested by: Daniel Rall <dlr@collab.net>

* subversion/tests/cmdline/svntest/testcase.py (XFail.__init__):
  Improve documentation and converted it from a comment to a
  docstring.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@859543 13f79535-47bb-0310-9956-ffa450edef68

YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,wbond/subversion,wbond/subversion,wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,wbond/subversion