Added extra test for contains key being given a value which is not also a key
Contains value assertion logic correct
Relaxed assertions to allow tests to pass under python 3.3 as well as python 3.1
Dictionary contains value method takes an optional userMessage argument.
User message is prepended to messages when exceptions are raised.
Added pydoc string to toContainValue method
Merge pull request #33 from iain-peddie/dict-contains-value

Dict contains value