import NodeError for usage in commands module

This also removes a few unused imports in the same module.
Merge pull request #28 from thobbs/node-error-import

import NodeError for usage in commands module
Make populate create balanced rings by default
Add debug option for create
Add 1k look-behind for mark_log
Add new stress path
Merge pull request #29 from driftx/master

Log marking is an optimization not really needed at startup and causes races.
Add offline scrub
Merge branch 'master' of github.com:pcmanus/ccm
Add drain command
Add support for the binary protocol
cast int to str to avoid TypeError
Don't ignore first arg when updating cluster conf
Merge pull request #30 from eevans/updateconf_typeerr

cast int to str to avoid TypeError
Merge pull request #31 from thobbs/cluster-update-conf-fix

Don't ignore first arg when updating cluster conf
Update for change of default partitioner in 1.2 (to murmur3)
Merge branch 'master' of github.com:pcmanus/ccm
Fix typo
Better handling of binary protocol
use /usr/bin/env to invoke python

since especially on OS X, the main python on the path (the one where
pyyaml is more likely to be installed, among other considerations)
may very well not be /usr/bin/python.