remove assertion preventing use of ncores with SlurmEnvironment.Command
Merge branch 'master' of github.com:nhoffman/bioscons
Merge branch 'dev'

Conflicts:
	bioscons/slurm.py
Wrapped results of SlurmEnvironment.__Slurm_Command in env.Precious
Set all_precious option (default: F) on slurm env initialization; precious behaviour can also be specified in commands
- prevent import error when SCons.Script is unavailable
- add fileutils.check_digest, fileutils.write_digest
increment version
Merge branch '9-all-precious' of https://github.com/metasoarous/bioscons into metasoarous-9-all-precious
update changelog for v0.6
Merge branch 'metasoarous-9-all-precious'
mention Precious feature in changelog
Fix for target-level precious=False

Previously, the per-target precious override worked for
all_precious=False and precious=True, but ignored the user override when
when all_precious=True and precious=False.