Bug fix: /# no longer matches foo.

17:49 < ral> Juerd: At least some of your tests are incorrect.
18:00 < ral> foo shouldn't match /# for example

Mosquitto rejects empty topics, but http://mqtt.org/wiki/doku.php/topic_format
says they're valid. If an empty topic is valid, it is the parent of /foo
and as such, it should match /# as well as # and +.