Bringing back some old code removed for hhvm, we do need it

src/Database/Driver/PDODriverTrait.php

@@ -93,6 +93,9 @@ public function prepare($query) {
  */
 	public function beginTransaction() {
 		$this->connect();
+		if ($this->_connection->inTransaction()) {
+			return true;
+		}
 		return $this->_connection->beginTransaction();
 	}
 
@@ -103,6 +106,9 @@ public function beginTransaction() {
  */
 	public function commitTransaction() {
 		$this->connect();
+		if (!$this->_connection->inTransaction()) {
+			return false;
+		}
 		return $this->_connection->commit();
 	}
 
@@ -112,6 +118,9 @@ public function commitTransaction() {
  * @return boolean true on success, false otherwise
  */
 	public function rollbackTransaction() {
+		if (!$this->_connection->inTransaction()) {
+			return false;
+		}
 		return $this->_connection->rollback();
 	}