First stab at a `reset_cluster` target.

Removes all engine modules that start with "distarray".

Probably needs refinement to get working fully.
reload -> reset
No longer `eval()` user command in ipcluster.py.
Merge branch 'master' into feature/reload-cluster

Conflicts:
	Makefile
Merge pull request #229 from enthought/feature/reload-cluster

First stab at a `reset_cluster` target.