There are historical reasons that the `plugin` command was `plugin_new`, now those are no longer applicable, we should remove the naming edge case from the project. This PR is based off of comments from #11176
ATP Railties
This is to avoid a conflict that occurs when you add Rake to
your Gemfile. There is a Commands Object in Rake that conflicts
with the Commands module in plugin.rb. See rails issue #1866.
* suppress outputting "Unknown command:" when no command were specified
* output the "Usage:" message when no plugin names were given
[#5043 state:committed]
Signed-off-by: Jeremy Kemper <jeremy@bitsweat.net>
schneems