Now double-click works also on really slow hardware. And Hatari.
Also, partially revert commit 01a2d2ed because events can't be passed
to the (multitasking) OS. So basically let's hope that it works fine now
even without handling IKBD overruns. I'm not able to replicate the issue
with Hatari + FF + slow UI + mouse movement anymore.
ScummVM engines are not built for synchronous screen locking (i.e.
updateScreen() can't be really used for any sort of blocking updates
otherwise performance suffers).
Single buffering now means deliberate tearing as a speed optimization
and triple buffering provides a tearingless picture with slight overhead.
