Do not cache follow sets if predicates are involved in a path

[mike-lischke]

The method processRule uses cached follow sets to speed up the walk process. This doesn't work if there's a predicate in one of the transitions while doing the walk. The transition path might depend on the outcome of that predicate.

Solution: don't cache follow sets if either a predicate is in the path taken or, if that cannot be determined efficiently, do not cache the sets at all.