Plugin install from Github should fail with a message if Git is not installed

Imported from Lighthouse. Original ticket at: http://rails.lighthouseapp.com/projects/8994/tickets/6530 Created by Matt Ryall - 2011-03-05 06:14:19 UTC

Working on a new machine, I didn't have git installed when I was trying to install a rails plugin. Unfortunately, the plugin installation fails silently with no indication of what is happening:

$ r plugin install git://github.com/toland/app_version.git
$

It would be great if this failed with a meaningful message instead. Even just 'git is not installed' would do it.

Several other people have also had the same problem:

• http://stackoverflow.com/questions/231390/installing-a-rails-plugin-from-a-git-repository
• http://stackoverflow.com/questions/1658139/plugins-not-getting-properly-installed