[ruby-core:33123] timer thread sleep interval (powertop abuses)

Hi everyone,

Some of this is covered in the issue tracker:

http://redmine.ruby-lang.org/issues/show/3436

powertop reports that ruby is triggering constant wakeups on linux,
which prevents us from doing proper power management.

I see a few ideas tossed around in the issue tracker, but it looks like
they are centered around preventing the timer thread when there is only
one thread.  We'll still want to cut down on wakeups even when there are
multiple threads.

Is the timer thread required for the threads to function?  Or is it only
there to deliver signals etc?  I've got ruby 1.9.1 patched here to just
poll every 500ms instead of every 10ms, which seems to work but I'm
guessing that if the easy way worked it would have already been done.

-chris