Fix problem with spurious Timer2B interrupt causing hangs.

(Or at least work-around the problem, I am still not sure why I get
the spurious interrupt in the first place, but detecting and ignoring
it makes things work).

Also throw in a couple of minor fixes.
Some few fixes for the Mivi board for POV control.

Mostly it is using 10MHz instead of 20MHz for reading back the
dot-correction values from the TLC5940's. For some reason this fails
at 20MHz sometimes; it appears to be a software-problem, but hard to
track down, and we do not need speed for checking dot-correction
values anyway.