…n the method table leaked out and caused issues for the user program.

In the cases that I've been able to repro, this happened because the bit got set for a short object right in front of a pinned plug, and then saved away by enque_pinned_plug.

Later on, in the case of mark & sweep, we check for the bit and reset it, but later we copy the saved object back by calling recover_saved_pinned_info which calls recover_plug_info to do the actual work. This isn't a problem for the compact case, because we copy the saved object back during compact_plug, turn the bit off, then save it again at the end of compact_plug.

The fix is to turn off the extra bits at the beginning of enque_pinned_plug and save_post_plug_info for the copy that is later restored in mark & sweep (there are actually two copies saved, one for use during compact and one for use during mark & sweep). This builds on an earlier fix by Maoni for a similar problem with another bit.

Added layer of abstraction and moved #ifdefs to lower levels.