Get a properly aliased_table_name, when we use a polymorphic association.

activerecord/lib/active_record/associations/association.rb

@@ -39,7 +39,7 @@ def initialize(owner, reflection)
       #   post.comments.aliased_table_name # => "comments"
       #
       def aliased_table_name
-        reflection.klass.table_name
+        klass.table_name
       end
 
       # Resets the \loaded flag to +false+ and sets the \target to +nil+.

activerecord/test/cases/associations/belongs_to_associations_test.rb

@@ -168,6 +168,7 @@ def test_polymorphic_association_class
 
     sponsor.sponsorable = Member.new :name => "Bert"
     assert_equal Member, sponsor.association(:sponsorable).send(:klass)
+    assert_equal "members", sponsor.association(:sponsorable).aliased_table_name
   end
 
   def test_with_polymorphic_and_condition