memoize_all fails when method has ? or ! at the end and arity > 0

Steps to reproduce:

1) define a class

      klass = Class.new
      klass.class_eval do
        extend ActiveSupport::Memoizable
        def can_memoize_question?(args)
          args
        end
        memoize :can_memoize_question?

        def memoize_bang!(args)
          args
        end
        memoize :memoize_bang!
      end

2) memoize_all

klass.new.memoize_all

3) delight the error

NameError: `@_memoized_memoize_bang!' is not allowed as an instance variable name