keep AssociationProxy#to_a to avoid warning in Array(post.author), and delegate it to @target in association collections

[#4165 state:committed]

Signed-off-by: Jeremy Kemper <jeremy@bitsweat.net>

activerecord/lib/active_record/associations/association_collection.rb

@@ -101,6 +101,7 @@ module ActiveRecord
           Array(@target)
         end
       end
+      alias_method :to_a, :to_ary
 
       def reset
         reset_target!

activerecord/lib/active_record/associations/association_proxy.rb

@@ -49,7 +49,7 @@ module ActiveRecord
       alias_method :proxy_respond_to?, :respond_to?
       alias_method :proxy_extend, :extend
       delegate :to_param, :to => :proxy_target
-      instance_methods.each { |m| undef_method m unless m =~ /(^__|^nil\?$|^send$|proxy_|^object_id$)/ }
+      instance_methods.each { |m| undef_method m unless m =~ /^(?:nil\?|send|object_id|to_a)$|^__|proxy_/ }
 
       def initialize(owner, reflection)
         @owner, @reflection = owner, reflection