Fixed #409.  Revised select-scroll accelerator to be time-based.

Here's the latest pull request for #409.  It's identical to the previous one, TingPing, except for the acceleration mechanism.  The short story is that my original design was flawed, ask me why if you like.  This design is time-based.  Acceleration only applies when you move the cursor vertically beyond a margin.  First for lines moved are at four lines/sec, next 8 at 8 lines/sec, next twelve at twice that, and after the 24th line (after three seconds, that is), acceleration is as fast as possible, with the timeout between lines set at 1 ms.

Arnavion, please check that this fixes 409 to your liking.  If I recall correctly, the last version did.