Reimplement type checks

[toirl]

Since version 0.5.1 the explicit type comparisions on operators like <, > != == etc has been removed.
The explicit tests has been implemented to ensure a defined behaviour among different versions of python. Unfortuantey the behaviour has changed between python 2.x and 3.x for some operators. Further it was a design decision to enforce the same type of values when doing operations.

In the current version of brabbel this isn't present anymore. I expect to get a Exception when trying to evaluate a expression when some types does not match.

[toirl]

There are currently no known issues with the missing typechecks. However I want them back to reestablish old behaviour and ensure that rules behave in the same way as before.

This issue is currently a blocker for 0.5.2 release.