brew outdated

brew install `brew outdated` will work

Apologies that this is long overdue.

Fixes Homebrew/homebrew#838

bin/brew

@@ -336,6 +336,22 @@ begin
     Dir.chdir HOMEBREW_REPOSITORY
     exec "cat", ARGV.formulae.first.path, *ARGV.options
 
+  when 'outdated'
+    require 'formula'
+    HOMEBREW_CELLAR.children.each do |keg|
+      if keg.subdirs.length > 0
+        name = keg.basename('.rb').to_s
+        if (not (f = Formula.factory(name)).installed? rescue nil)
+          if $stdout.tty? and not ARGV.flag? '--quiet'
+            versions = keg.cd{ Dir['*'] }.join(', ')
+            puts "#{name} (#{versions} < #{f.version})"
+          else
+            puts name
+          end
+        end
+      end
+    end
+
   else
     onoe "Unknown command: #{arg}"
   end