All tests pass with SVN 1.6. SVN 1.7 remains broken, not worrying
about it yet.
SVN changed its path canonicalization API between 1.6 and 1.7.
http://svnbook.red-bean.com/en/1.6/svn.developer.usingapi.html#svn.developer.usingapi.urlpath
http://svnbook.red-bean.com/en/1.7/svn.developer.usingapi.html#svn.developer.usingapi.urlpath
The SVN API does not accept foo/.. but it also doesn't canonicalize
it. We have to do it ourselves.
[ew: commit title, fall back if SVN <= 1.6 fails to canonicalize]