Revert "removing crazy finalizer code until there is proof that we need it"

This reverts commit a40e3c1a96.

actionpack/lib/action_view/template.rb

@@ -101,6 +101,16 @@ module ActionView
     attr_reader :source, :identifier, :handler, :virtual_path, :formats,
                 :original_encoding
 
+    # This finalizer is needed (and exactly with a proc inside another proc)
+    # otherwise templates leak in development.
+    Finalizer = proc do |method_name, mod|
+      proc do
+        mod.module_eval do
+          remove_possible_method method_name
+        end
+      end
+    end
+
     def initialize(source, identifier, handler, details)
       @source             = source
       @identifier         = identifier
@@ -245,6 +255,7 @@ module ActionView
 
         begin
           mod.module_eval(source, identifier, 0)
+          ObjectSpace.define_finalizer(self, Finalizer[method_name, mod])
 
           method_name
         rescue Exception => e # errors from template code