CFG: Bug in production of the merge block when having #continue and #break statements if conditionals

[jecisc]

I am adding the concept of #mergeBlock to the CFG, especially for Python.

A merge block for a conditional block is the first node present in all branches of the condition.
It means that it is the first node following the conditional statement (if, switch, for, while, try...)

I managed most cases, but I detected a bug in the way I handled it when we have break and continue statements in the branches of a conditional in a loop.

I'll not have the time to fix it for now, but I want to keep a trace of this issue.

We should carefully review how merge points should be managed in those cases to cover those.

[jecisc]

If we do that, we should add the missing assertions in FAST-Python in the tests. I added test on all working merge blocks resolution but not for this