Use *_transaction methods in TransactionManager

Use `commit_transaction`/`rollback_transaction` on
`within_new_transaction` method, so they make sure they `pop` the
transaction from the stack before calling the methods `commit`/`rollback`.

activerecord/lib/active_record/connection_adapters/abstract/transaction.rb

@@ -169,16 +169,14 @@ module ActiveRecord
         transaction = begin_transaction options
         yield
       rescue Exception => error
-        transaction.rollback if transaction
+        rollback_transaction if transaction
         raise
       ensure
         begin
-          transaction.commit unless error
+          commit_transaction unless error
         rescue Exception
           transaction.rollback
           raise
-        ensure
-          @stack.pop if transaction
         end
       end
 

activerecord/test/cases/transactions_test.rb

@@ -80,6 +80,30 @@ class TransactionTest < ActiveRecord::TestCase
     end
   end
 
+  def test_number_of_transactions_in_commit
+    num = nil
+
+    Topic.connection.class_eval do
+      alias :real_commit_db_transaction :commit_db_transaction
+      define_method(:commit_db_transaction) do
+        num = transaction_manager.open_transactions
+        real_commit_db_transaction
+      end
+    end
+
+    Topic.transaction do
+      @first.approved  = true
+      @first.save!
+    end
+
+    assert_equal 0, num
+  ensure
+    Topic.connection.class_eval do
+      remove_method :commit_db_transaction
+      alias :commit_db_transaction :real_commit_db_transaction rescue nil
+    end
+  end
+
   def test_successful_with_instance_method
     @first.transaction do
       @first.approved  = true