Fix nasty bug in pg.bufferPulse
Fix nasty bug in pg.bufferPulse

Pulse turn offs were being ignored because the diff() of a uint vector
cannot be negative. Furthermore, we were not properly handling the case
of just two marker pulses.
--BRJ

BBN-Q/Qlab,BBN-Q/Qlab,Plourde-Research-Lab/Qlab,rmcgurrin/Qlab,rmcgurrin/Qlab,BBN-Q/Qlab,BBN-Q/Qlab,Plourde-Research-Lab/Qlab,rmcgurrin/Qlab,Plourde-Research-Lab/Qlab,rmcgurrin/Qlab