added supportsReleaseSavepoints(), disabled releasing for Oracle and DB2...

added supportsReleaseSavepoints(), disabled releasing for Oracle and DB2 (already disabled for MSSQL

lib/Doctrine/DBAL/Connection.php

@@ -900,9 +900,8 @@ class Connection implements DriverConnection
             ConnectionException::savepointsNotSupported();
         }
 
-        $sql = $this->_platform->releaseSavePoint($savepoint);
-        if ($sql) {
-            $this->_conn->exec($sql);
+        if ($this->_platform->supportsReleaseSavepoints()) {
+            $this->_conn->exec($this->_platform->releaseSavePoint($savepoint));
         }
     }
 

lib/Doctrine/DBAL/Platforms/AbstractPlatform.php

@@ -1773,6 +1773,16 @@ abstract class AbstractPlatform
         return true;
     }
 
+    /**
+     * Whether the platform supports releasing savepoints.
+     *
+     * @return boolean
+     */
+    public function supportsReleaseSavepoints()
+    {
+        return $this->supportsSavepoints();
+    }
+
     /**
      * Whether the platform supports primary key constraints.
      *

lib/Doctrine/DBAL/Platforms/DB2Platform.php

@@ -291,6 +291,16 @@ class DB2Platform extends AbstractPlatform
         return false;
     }
 
+    /**
+     * Whether the platform supports releasing savepoints.
+     *
+     * @return boolean
+     */
+    public function supportsReleaseSavepoints()
+    {
+        return false;
+    }
+
     /**
      * Gets the SQL specific for the platform to get the current date.
      *

lib/Doctrine/DBAL/Platforms/OraclePlatform.php

@@ -659,6 +659,16 @@ LEFT JOIN all_cons_columns r_cols
         return false;
     }
 
+    /**
+     * Whether the platform supports releasing savepoints.
+     *
+     * @return boolean
+     */
+    public function supportsReleaseSavepoints()
+    {
+        return false;
+    }
+
     /**
      * @inheritdoc
      */