unicorn 4.1.1 - fix last-resort timeout accuracy

The last-resort timeout mechanism was inaccurate and often
delayed in activation since the 2.0.0 release.  It is now fixed
and remains power-efficient in idle situations, especially with
the wakeup reduction in MRI 1.9.3+.

There is also a new document on application timeouts
intended to discourage the reliance on this last-resort
mechanism.  It is visible on the web at:

  http://unicorn.bogomips.org/Application_Timeouts.html