Better memory usage

We’ve made two changes to DISCOVAR de novo:

1. Memory usage during BAM file reading is now lower.

2. We’ve added a memory check to see how much memory appears to be available, and then throttle memory usage to that level. Sometimes (and particularly on scheduled systems like SGE) the amount of available memory is reduced. Please let us know if you observe aberrant behavior. The feature can be turned off by setting MEMORY_CHECK=False on the DiscoverExp command line.