Add 'remote' argument to heroku

Also add the shorter -a switch to the app argument
Add remote argument completions

This was copied from _git-flow
_brew update

1. use _call_program
2. formulae completion for search
3. formulae completion for upgrade
4. add pin/unpin command
Namespace git commands under heroku
Merge pull request #128 from pcasaretto/add-remote-argument-to-heroku

Add 'remote' argument to heroku
Merge pull request #133 from zhaocai/brew

_brew update
Merge pull request #134 from zhaocai/feature/_gem

_gem: update for browse, edit and clone commands
Update ack to work with version 2+
Add `open` command for _gem
Merge branch 'master' into feature/_gem