fixes regression introduced by PR 1720 (#1733)

it seems there was a typo in #1720, this should fix it.

Author: fballiano

lib/Varien/Db/Adapter/Pdo/Mysql.php

@@ -2640,7 +2640,7 @@ public function isTableExists($tableName, $schemaName = null)
             $this->quote($tableName),
             $fromDbName
         );
-        $ddl = $this->rawFetchRow($sql, 'tbl_exists');
+        $ddl = $this->raw_FetchRow($sql, 'tbl_exists');
         if ($ddl) {
             return true;
         }