Add some testcases for svn_path* functions.
Add some testcases for svn_path* functions.

Note that one of the testcases shows that our use of svn_path functions on both
urls and dir entries is neither well documented nor correct. Solving issue 
#1711 should fix this.

* subversion/tests/libsvn_subr/path-test.c
  (test_path_is_ancestor): Add some new testcases.
  (test_get_longest_ancestor): ... And here too.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion