Rework LazynessAnalysis

* This analysis was hard to understand
* It was not correct on many point (function arguments for example
  and use to many uncorrect aliasing)
Fix test to have less random result
Merge pull request #228 from pbrunet/rework_lazy_aliasing

Rework lazy aliasing
Add omp statement in unparse
Add a new way to test optimization

* Check if the output is the one expected
Code factorisation for Pythran frontend