Properly detect redundant parameter exceptions

[SoongNoonien]

As it has been seen in #51 there are places in the code where parameter exceptions are only returned after a (possibly partial) check for redundancy. It would be much better if there were a nicely documented function which decides if a parameter exception is redundant. And by redundant I mean if it isn't possibly for the exception to apply, so for example an exception 1//2+i ∈ ℤ can safely be ignored.
But it is worth noting that 1//2+i ∈ ℤ shouldn't occur in the first place as we usually deal with "reduced" polynomials where reduced means without integral part.

[SoongNoonien]

Also it might be worth reconsidering if a set is really the best data structure to store the exceptions. We need to compare the exceptions pairwise anyway to decide if they imply one another.

[SoongNoonien]

With #155 the situation here improves. At least for all pairs of exceptions all cancellation should now be detected. But there are still exceptions which are never an integer but aren't irgnored. For example $\frac{3}{4} \in \mathbb{Z}$ or $\frac{1}{q+2} \in \mathbb{Z}$. Though I'm not sure if those can occur in the first place.

[fingolfin]

Can we address this similar to what I describe in #177 ? I.e. $\frac{3}{4} \in \mathbb{Z}$ or $\frac{1}{q+2} \in \mathbb{Z}$ can be rewritten as $3 \in 4\mathbb{Z}$ or $1 \in (q+2)\mathbb{Z}$. And then trick to "factor the left side, kill any factors that are invertible modulo the right side simplifies the first to $1 \in 4\mathbb{Z}$.

Then finally, kill anything of the form c \in n \mathbb{ZZ} if c is an integer constant (here: 1) and the right hand modulus n is provably > 1. This is trivial in your examples. Of course it can be trickier if the modulus is e.g. $q-3$. In that case we actually do get a special case for $q=4$. And of course it can be more complicated...

That said, my instinct would be to close this for now as resolved, and open a new issue for concrete instances as they crop up. Most likely working towards the long-term vision outlined in #28 will yield more relevant examples