PostgreSQL: comparing string and integer

There's one issue causing this module from working properly with PostgreSQL. There's a comparision with strings and integers in the code, more specifically period = 2. In MySQL comparing integers with strings will perform an implicit type convertion. In PostgreSQL however this is illegal and causes an error:

PDOException: SQLSTATE[42883]: Undefined function: 7 ERROR: operator does not exist: character varying = integer

The attached patch will properly quote the values so they are strings instead. This has been tested on a site.