bamPEFragmentSize is crazy with memory

[dpryan79]

With a bunch of BAM files this thing can gobble up memory like a fat kid at a buffet. But that makes no sense, since the only thing it should be keeping in memory is a list of fragment sizes (even that we could presumably store with some sort of run length encoding). I suspect what's happening is that it never frees memory after processing a BAM file, thus increasing to crazy amounts before it finishes (or gets killed). This should really be fixed though.