Second bite at the rules-only idea

This is part 2 of the patch that improved the interaction of RULES and
recursion.  It's vital that all Ids that may be referred to from later in
the module are marked 'IAmALoopBreaker' because otherwise we may do
postInlineUnconditionally, and lose the binding altogether.

So I've added a boolean rules-only flag to IAmALoopBreaker.  Now we can
do inlining for rules-only loop-breakers.