Fix performance bug in AttibuteMethods#respond_to? in handling of pri…

…vate methods

We have hit dramatic increase in tests time after upgrading rails.
Profiling revealed this particular place. After this fix our test times returned
back to norm.

Signed-off-by: Michael Koziarski <michael@koziarski.com>
[#1173 state:committed]

activerecord/lib/active_record/attribute_methods.rb

@@ -342,7 +342,9 @@ def respond_to?(method, include_private_methods = false)
       method_name = method.to_s
       if super
         return true
-      elsif self.private_methods.include?(method_name) && !include_private_methods
+      elsif !include_private_methods && super(method, true)
+        # If we're here than we haven't found among non-private methods
+        # but found among all methods. Which means that given method is private.
         return false
       elsif !self.class.generated_methods?
         self.class.define_attribute_methods