Improve error reporting.
Improve error reporting.

* subversion/tests/cmdline/svntest/tree.py
  (detect_conflict_files): Improve error message text/formatting, and
   include the message in the exception thrown by the function.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@866643 13f79535-47bb-0310-9956-ffa450edef68

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