Revert a previous incorrect fix for the PIT.
Modify the PitDecrementCount function to take a parameter instead
of it being called multiple times (which is slower).
svn path=/branches/ntvdm/; revision=60816
Improve performance by computing the resolution required by the PIT,
and then using the standard tick count instead of performance counters
when that resolution is low.
svn path=/branches/ntvdm/; revision=60783
