New command brew irb

Works rather damn well.

I considered `brew -i`, but we aren't a shell.

Library/Homebrew/cmd/irb.rb

@@ -0,0 +1,11 @@
+module Homebrew extend self
+  def irb
+    if ARGV.include? "--help"
+      puts "Formula.factory('ace').installed?"
+    else
+      ohai "Interactive Homebrew Shell"
+      puts "Example commands available with: brew irb --help"
+      exec "irb", "-I#{HOMEBREW_REPOSITORY}/Library/Homebrew", "-rglobal"
+    end
+  end
+end