Add new testcases for svn_path_get_longest_ancestor.
Add new testcases for svn_path_get_longest_ancestor.

* subversion/tests/libsvn_subr/path-test.c
  (test_get_longest_ancestor): New test cases. Run the testcases also in 
   with path1 and path2 in different order, svn_path_get_longest_ancestor
   is supposed to be order-independent.

git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@862157 13f79535-47bb-0310-9956-ffa450edef68

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