DriverContext.getOperatorPreAllocatedMemory uses parent context's getOperatorPreAllocatedMemory
Disable dependency version check in presto-server

The dependency checker is incorrectly looking at depencies of
bundled plugins
Update to airlift 0.89-SNAPSHOT
Use TimeStat for measuring times

TimeStat allows controlling the unit used to display the measurements
via JMX and exposes the unit as another mbean attribute

This fixes the issue where pXX stats show -Long.MAX_VALUE when there are no
measurements. It now displays NaN, instead.