Make it possible to retrieve all properties in toDict
We used to retrieve only the properties that are specified in the
self.properties() dictionary, instead, we now iterate over the
key_fields and only use self.properties() if those are not specified.
Patch by: Sverre Rabbelier
Coverage: code coverage testing for Python
Coverage.py is a Python module that measures code coverage during test execution.
It uses the code analysis tools and tracing hooks provided in the Python standard
library to determine which lines are executable, and which have been executed.
For more information, see http://nedbatchelder.com/code/modules/coverage.html