Fix #1709: do not expose the worker for a loop-breaker
The massive 'Uni' program produced a situation in which a function that had a worker/wrapper split was chosen as a loop breaker. If the worker is exposed in the interface file, then an importing module may go into an inlining loop: see comments on TidyPgm.tidyWorker. This patch fixes the inlining bug. The code that gives rise to this bizarre case is still not good (it's a bunch of implication constraints and we are choosing a bad loop breaker) but the first thing is to fix the bug. It's rather hard to produce a test case! Please merge to the 6.8 branch.