Adjust turbo speed threshold to be more forgiving.

The gatevalve closes when the turbo slows down, with the turbo configured to drop a hardware signal at a configured fraction of the maximum speed (90000 rpm). With one cryostat on the roughing line, it has been reliable with the threshold set to the maximum of 99% – the notion being that if anything goes wrong on the roughing line we want to close ASAP. 

But with two cryostats at IDG it is clear that threshold is too high: it takes almost nothing to drop the speed a hair.

So lower to 90-95% – a bit of testing will clarify.