4436: Don't handle SIGTERM for glidefactoryEntryGroup children

The children don't need to do any cleanup, and there's an unavoidable
race with asynchronous exceptions. We handle this by unregistering
the signal handler before we fork the child (and re-registering as soon
as we can.)
4436: Remove race in write_stats children

We unregister the signal handler in write_stats children, but only
after the fork, so there could be a race if an exception arrives before
the handler is deregistered.

We now unregister right before the fork (and re-register the parent right
after).
Merge branch 'v2/4436' into branch_v2plus