Refactor the IsInt keys for filter scanning

[sebasguts]

In the IsInt case for scanning filters is a whole lot of effort put in for detection of KeyDependentOperation. If one would store if a KeyDependentOperation is scanned, this can be simplified.

[fingolfin]

@sebasguts What's the status of this? I am not even sure I understand what it is about...

[sebasguts]

Sorry, this description is mediocre. I am talking about this if here. KeyDependentOperation is the only declaration that has two filter arguments, and not a single filter or a list, therefore I handle it differently. I wanted to refactor this.

[fingolfin]

I think the point Sebastian was trying to make here back then is that the only two integer values for has_filters are 1 and 2, but 2 only appears in one place, namely for KeyDependentOperation. Yet the code for handling integer has_filters values is fully generic.

Or maybe that wasn't the point exactly; it doesn't matter, I guess, the code has changed quite a bit since then and will change further soon enough.