Fix brew/init
Fix brew/init

* Check existence of the brew command before calling it;
* Regen paths after installing Homebrew;
* Strip potential tap prefix when calculating formula name from an
  option string;
* Perform word splitting on the option string.

zmwangx/dotfiles,zmwangx/dotfiles,zmwangx/dotfiles,zmwangx/dotfiles,zmwangx/dotfiles