Add ruby/rake functions to use system framework version.

Library/Homebrew/formula.rb

@@ -290,6 +290,18 @@ class Formula
     ]
   end
 
+  def ruby_bin
+    '/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin'
+  end
+
+  def rake *args
+    system "#{ruby_bin}/rake", *args
+  end
+
+  def ruby
+    system "#{ruby_bin}/ruby", *args
+  end
+
   def self.class_s name
     #remove invalid characters and then camelcase it
     name.capitalize.gsub(/[-_.\s]([a-zA-Z0-9])/) { $1.upcase } \