Ensure coverage calculations occur within transaction and avoid re-running if present
Improve memory usage for samtools during bwa alignment steps. Avoid over-scheduling memory by sharing between sort in, bwa, and sort out steps
Add documentation on new memory management framework and relationship with job scheduling
Merge branch 'master' of https://github.com/chapmanb/bcbio-nextgen
Release v0.7.2
Provide useful error messages when merging and number of files exceeds system ulimit. Fixes #96