ListLike.drop: improved strictness and behavior
ListLike.drop: improved strictness and behavior

ListLike.drop is now a nop for predicates < 0.
Performance is improved by two additions:
  1. The null check has been removed within the step function (it's entirely
  subsumed by the other two cases).
  2. The amount to drop is made strict (I think this is a regression in
  ghc-7.6).

JohnLato/iteratee