Make Set available globally

Signed-off-by: Jack Nagel <jacknagel@gmail.com>

Library/Homebrew/cmd/doctor.rb

@@ -1,4 +1,3 @@
-require 'set'
 require 'cmd/missing'
 
 class Volumes

Library/Homebrew/dependencies.rb

@@ -1,5 +1,3 @@
-require 'set'
-
 ## This file defines dependencies and requirements.
 ##
 ## A dependency is a formula that another formula needs to install.

Library/Homebrew/formula_installer.rb

@@ -1,7 +1,6 @@
 require 'exceptions'
 require 'formula'
 require 'keg'
-require 'set'
 require 'tab'
 require 'bottles'
 

Library/Homebrew/global.rb

@@ -3,6 +3,7 @@ require 'extend/ARGV'
 require 'extend/string'
 require 'utils'
 require 'exceptions'
+require 'set'
 
 ARGV.extend(HomebrewArgvExtension)