prevent changing savepoint behavior inside an open transaction

lib/Doctrine/DBAL/Connection.php

@@ -754,6 +754,10 @@ class Connection implements DriverConnection
      */
     public function setNestTransactionsWithSavepoints($nestTransactionsWithSavepoints)
     {
+        if ($this->_transactionNestingLevel > 0) {
+            throw ConnectionException::mayNotAlterNestedTransactionWithSavepointsInTransaction();
+        }
+
         if ($nestTransactionsWithSavepoints && !$this->_platform->supportsSavepoints()) {
             ConnectionException::savepointsNotSupported();
         }

lib/Doctrine/DBAL/ConnectionException.php

@@ -46,4 +46,9 @@ class ConnectionException extends DBALException
     {
         return new self("Savepoints are not supported transaction.");
     }
+
+    public static function mayNotAlterNestedTransactionWithSavepointsInTransaction()
+    {
+        return new self("May not alter the nested transaction with savepoints behavior while a transaction is open.");
+    }
 }
\ No newline at end of file

tests/Doctrine/Tests/DBAL/Functional/ConnectionTest.php

@@ -77,6 +77,12 @@ class ConnectionTest extends \Doctrine\Tests\DbalFunctionalTestCase
                     //no rethrow
                 }
                 $this->assertFalse($this->_conn->isRollbackOnly());
+                try {
+                    $this->_conn->setNestTransactionsWithSavepoints(false);                    
+                    $this->fail('Should not be able to disable savepoints in usage for nested transactions inside an open transaction.');
+                } catch (ConnectionException $e) {
+                    $this->assertTrue($this->_conn->getNestTransactionsWithSavepoints());
+                }
                 $this->_conn->commit(); // should not throw exception
             } catch (ConnectionException $e) {
                 $this->fail('Transaction commit after failed nested transaction should not fail when using savepoints.');