Panic with local definiton that uses constraint guards without a type signature about cryptol

[RyanGlScott]

This issue involves checkNumericConstraintGuardsOK. This function makes the assumption that by the time it is invoked, all numeric constraint guard expressions have been checked to have a type signature. (See the comment here.) This isn't actually true, however. The code in Cryptol.Parser.ExpandPropGuards does check that top-level numeric constraint guards have type signatures, but it does not check any constraint guards in where expressions.

Two ways we could fix this:

1. Make Cryptol.Parser.ExpandPropGuards recurse into where expressions and reject any nested constraint guards it encounters. (This would make this error message later in the typechecker unreachable, so we could remove it.)
2. Do not assume that by the time checkNumericConstraintGuardsOK is invoked, we have checked all constraint guards to have a type signature.

I am leaning more towards option (1), since this is the sort of thing that we could easily detect (and reject) in the parser, well before we get to the typechecker.

[yav]

Yeah, I also think (1) is the way to go.