Documentation improvements for the blackbox merge test.
Documentation improvements for the blackbox merge test.

* subversion/tests/cmdline/merge_tests.py
  (setup_dir_replace): Improve doc string and inline comments.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@863244 13f79535-47bb-0310-9956-ffa450edef68

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