use respond_to? rather than arity checks to play nice with method_mis…

…sing proxies

Conflicts:

	lib/sinatra/base.rb
	test/delegator_test.rb

lib/sinatra/base.rb

@@ -1478,14 +1478,7 @@ def self.delegate(*methods)
       methods.each do |method_name|
         eval <<-RUBY, binding, '(__DELEGATE__)', 1
           def #{method_name}(*args, &b)
-            arity = ::Sinatra::Delegator.target.method(#{method_name.inspect}).arity
-            if arity < 0 ? args.size < -arity - 1 : args.size != arity
-              begin
-                return super
-              rescue NameError => e
-                raise e unless e.message.include? #{method_name.to_s.inspect}
-              end
-            end
+            return super if respond_to? #{method_name.inspect}
             ::Sinatra::Application.send(#{method_name.inspect}, *args, &b)
           end
           private #{method_name.inspect}