Make an update test a bit clearer.
Make an update test a bit clearer.

* subversion/tests/cmdline/update_tests.py
  (forced_update_failures): Rework how the test works to make it a bit
  clearer.  Dump some thoughts related to issue #3209 into the comment.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@875408 13f79535-47bb-0310-9956-ffa450edef68

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