Currently if you don't specify the '-m' option, a fake do-nothing memory
profiler thread gets created instead of the real one. It ignores all
events except for `Exit`. And the timer thread doesn't get created so no
`Print` events are sent.
This changeset instead always creates the real thread. If you specify
'-m' the *timer* thread is still absent and it won't print anything.
However, the memory profiler thread will respond to register/unregister
events, which is good, because if there's a bug in those (e.g.
double-registration of a particular name) it'll show up in invocations
that lack '-m'.
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