Before download errors, output source and location

[justincampbell]

Fixes #145

Installing ohai (1.1.2) from site: 'http://cookbooks.opscode.com/api/v1/cookbooks'
Failed to download doesntexist from git: 'git://github.com/asdjhfkljashflkjashfakljsf'
An error occured during Git execution:

[reset]

you can actually write this

rescue
  # something
  raise
end

[reset]

👍 looks good!

[justincampbell]

@reset Awesome, updated it