ENH: Throttle number of qstat commands in SGE and manage the queue better

ENH: Large SGE jobs were DOS on qsub

When large jobs were run with SGE, the accumulation of
qstat queries was causing a massive load on the cluster
server, and was affecting overal system performance.

This modifications keeps track of when qsub was last run
for a particular job, and slowly throttles each job back
so that qsub is called on a more reasonable time frame.