Allow vendored frameworks to override built-in frameworks to enable

testing and development.

lib/compass/frameworks.rb

@@ -28,8 +28,12 @@ module Compass
     end
 
     def register(name, *arguments)
+      if idx = ALL.index{|f| f.name.to_s == name.to_s}
+        ALL[idx] = Framework.new(name, *arguments)
+      else
         ALL << Framework.new(name, *arguments)
       end
+    end
 
     def [](name)
       ALL.detect{|f| f.name.to_s == name.to_s}