_newresource.py: remove obsolete todo
_newresource.traverse: implement the non-deferred case
t.w.test_newresource: use successResultOf instead of returning deferred
t.web._newresource.traverse: handle deferred traversal
t.web.test_newresource: test multiple-segment traversal
t.web.test_newresource: add test for zero-segment resource
t.web.test_newresource: correct copy/pasted docstrings