Removes the restriction on primary key when joining in a habtm && test that it was properly removed

activerecord/lib/active_record/associations.rb

@@ -76,12 +76,6 @@ def initialize(owner, reflection)
     end
   end
 
-  class HasAndBelongsToManyAssociationWithPrimaryKeyError < ActiveRecordError #:nodoc:
-    def initialize(reflection)
-      super("Primary key is not allowed in a has_and_belongs_to_many join table (#{reflection.options[:join_table]}).")
-    end
-  end
-
   class HasAndBelongsToManyAssociationForeignKeyNeeded < ActiveRecordError #:nodoc:
     def initialize(reflection)
       super("Cannot create self referential has_and_belongs_to_many association on '#{reflection.class_name rescue nil}##{reflection.name rescue nil}'. :association_foreign_key cannot be the same as the :foreign_key.")

activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb

@@ -39,10 +39,6 @@ def check_validity(reflection)
           model.send(:undecorated_table_name, model.to_s),
           model.send(:undecorated_table_name, reflection.class_name)
         )
-
-        if model.connection.supports_primary_key? && (model.connection.primary_key(reflection.options[:join_table]) rescue false)
-          raise ActiveRecord::HasAndBelongsToManyAssociationWithPrimaryKeyError.new(reflection)
-        end
       end
 
       # Generates a join table name from two provided table names.

activerecord/test/cases/associations/habtm_join_table_test.rb

@@ -33,12 +33,11 @@ def teardown
     ActiveRecord::Base.connection.drop_table :my_books_my_readers
   end
 
-  uses_transaction :test_should_raise_exception_when_join_table_has_a_primary_key
-  def test_should_raise_exception_when_join_table_has_a_primary_key
+  uses_transaction :test_should_not_raise_exception_when_join_table_has_a_primary_key
+  def test_should_not_raise_exception_when_join_table_has_a_primary_key
     if ActiveRecord::Base.connection.supports_primary_key?
-      assert_raise ActiveRecord::HasAndBelongsToManyAssociationWithPrimaryKeyError do
-        MyReader.has_and_belongs_to_many :my_books
-      end
+      # This test is to confirm that this feature is now gone 
+      assert MyReader.has_and_belongs_to_many(:my_books).is_a?(ActiveRecord::Reflection::AssociationReflection)
     end
   end
 end