Merge commit 'origin/next' into branch-2.1

* commit 'origin/next':
  Fix gnt-node modify online help
  Fix gnt-job info entry in gnt-job(8)
  locking: Don't swallow exceptions
  Add check for duplicate MACs in instance add
  scripts/gnt-node: fix a help string
  Optimise multi-job submit
  Extend gnt-debug with more debugging options

Conflicts:
	scripts/gnt-debug: Trivial
	scripts/gnt-node: Trivial