[PATCH] Class and Module are duplicable

In active_support/core_ext/object/duplicable.rb says that either Class and Module are not duplicable.
If you run on the console:

Class.new.duplicable?
 => false 
Module.new.duplicable?
 => false

but, if you do

Class.new.dup
 => #<Class:0x00000102983160>
Module.new.dup
 => #<Module:0x00000102976988>

Also DuplicableTest is not really testing if it raises an Exception.
Marked Class and Module as duplicable (as they are now) and fixed the test.