Fix state being carried over from previous transaction

This clears the transaction record state when the transaction finishes
with a `:committed` status.

Considering the following example where `name` is a required attribute.
Before we had `new_record?` returning `true` for a persisted record:

```ruby
  author = Author.create! name: 'foo'
  author.name = nil
  author.save        # => false
  author.new_record? # => true
```

1 files changed, 7 insertions, 0 deletions

diff --git a/activerecord/test/cases/transactions_test.rb b/activerecord/test/cases/transactions_test.rb
index 4e163ca4a6..29a6ec7522 100644
--- a/activerecord/test/cases/transactions_test.rb
+++ b/activerecord/test/cases/transactions_test.rb
@@ -175,6 +175,13 @@ class TransactionTest < ActiveRecord::TestCase
     assert topic.new_record?, "#{topic.inspect} should be new record"
   end
 
+  def test_transaction_state_is_cleared_when_record_is_persisted
+    author = Author.create! name: 'foo'
+    author.name = nil
+    assert_not author.save
+    assert_not author.new_record?
+  end
+
   def test_update_should_rollback_on_failure
     author = Author.find(1)
     posts_count = author.posts.size