Support running 1.6.x tests against a 1.5.x server.
Support running 1.6.x tests against a 1.5.x server.

* subversion/tests/cmdline/svntest/main.py
  (server_minor_version): Default value is now 6.
  (create_repos): Use --pre-1.6-compatible if appropriate.
  (run_tests): Support a value of 6.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@876016 13f79535-47bb-0310-9956-ffa450edef68

YueLinHo/Subversion,wbond/subversion,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