Following up on r1674600, avoid testing the same thing twice and add a few more edge cases.
Following up on r1674600, avoid testing the same thing twice and
add a few more edge cases.

* subversion/tests/cmdline/diff_tests.py
  (diff_incomplete): Extend test.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@1674602 13f79535-47bb-0310-9956-ffa450edef68

YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion