title: Git completion including flags with bash aliases
body: <p>I have git completion working with my bash aliases</p>
  
  <p><em>~/.bash_profile</em></p>
  
  <pre><code>if [ -f $(brew --prefix)/etc/bash_completion ]; then
    source $(brew --prefix)/etc/bash_completion.d/git-completion.bash
  fi
  
  alias gco='git checkout'
  __git_complete gco _git_checkout
  </code></pre>
  
  <p>How can I do a <code>__git_complete</code> for a git command with a flag?</p>
  
  <pre><code>alias gcb='git checkout -b'
  </code></pre>