Better ruby interpreter compatibility

This is partly a regression from a jruby fix that
has been applied some time ago

  See http://is.gd/b7fGz

Also, it solves the following issue on ruby-1.9

  Implicit argument passing of super from method
  defined by define_method()

[#1228 state:resolved]

lib/dm-rails/railties/benchmarking_mixin.rb

@@ -2,14 +2,15 @@ module DataMapper
   module Adapters
     module Benchmarking
 
-      %w(create read update delete).each do |method|
-
-        define_method method do |*args, &block|
-          result = nil
-          @runtime ||= 0
-          @runtime += Benchmark.ms { result = super }
-          result
-        end
+      %w[ create read update delete ].each do |method|
+        class_eval <<-RUBY, __FILE__, __LINE__
+          def #{method}(*args, &block)
+            result = nil
+            @runtime ||= 0
+            @runtime += Benchmark.ms { result = super(*args, &block) }
+            result
+          end
+        RUBY
       end
 
       def reset_runtime