Allow overriding of ey-deploy version.
Allow overriding of ey-deploy version.

If you set ENV["EY_DEPLOY_VERSION"] before invoking 'ey', it will use
the specified version of ey-deploy.

This is mainly useful for development; this way, you can test out your
ey-deploy changes without having to edit the source of your installed
engineyard gem.

[#138]

radamanthus/engineyard,engineyard/engineyard,engineyard/engineyard,radamanthus/engineyard,cowboyd/engineyard