Allow opting out of Homebrew and casks.
Reorganize osx/devel init and source scripts.
dotfiles script: init after copy and link.
Better detect osx default shell.
Fix homebrew headers.
Test for brew-cask before running it.
Update brew cask listing logic.
Update RftG cask.
Add sudo keep-alive script.
Tweak sudo keep-alive script.
Remove crazy sudo keep-alive thing. It's useless.
Move sudo stuff to the very end, where possible.
Show first-time brew-cask password immediately.
Improve to_install function.
Merge remote-tracking branch 'upstream/master'

* upstream/master:
  Improve to_install function.
  Show first-time brew-cask password immediately.
  Move sudo stuff to the very end, where possible.
  Remove crazy sudo keep-alive thing. It's useless.
  Tweak sudo keep-alive script.
  Add sudo keep-alive script.
  Update RftG cask.
  Update brew cask listing logic.
  Test for brew-cask before running it.
  Fix homebrew headers.
  Better detect osx default shell.
  dotfiles script: init after copy and link.
  Reorganize osx/devel init and source scripts.
  Allow opting out of Homebrew and casks.

Conflicts:
	source/50_node.sh
Added composer in separate file