Add autocompletion for Rails3.

+ Originally published by Christopher Chow.
+ Source:
https://github.com/robbyrussell/oh-my-zsh/blob/30620d463850c17f86e7a56fbf6a8b5e793a4e07/plugins/rails3/_rails3
  Commit: 30620d463850c17f86e7a56fbf6a8b5e793a4e07
Change duplicated alias name
rvm plugin: update to ruby version helpers and rvm-update

* the current patch levels hard-coded here are pretty dated. I updated the ruby version helpers to use loose ruby version matchers so they don't continually need to be updated with every new patch level release.

* `rvm get head` actually performs an `rvm reload` in the post install. there's no need to do again here in rvm-update so I've removed that.
The current version of bower is completely unavailable, plugin depth modification
Update coffee completion
fixed typo in tmux plugin
Fix ssh-agent plugin identities comment for using multiple identities.
Add knife_ssh command to make connecting to servers managed with chef easier
No cat, and hide errors for missing cache file
Added autocompletion support for Elixir mix command
Fix symfony command completion 'permission denied'
In capistrano completion show also tasks without description
Updated gem plugin zsh completion (gem 2.0.3).
Make glg git log output pretty