Don't die horribly from sql.php when making INSERT/DELETE/UPDATE/CREATE TABLE/etc...

Don't die horribly from sql.php when making INSERT/DELETE/UPDATE/CREATE TABLE/etc calls that return 'true' instead of a result object.
Code was attempting to handle this case by asking the result object for its db so we can ask for the affected row count -- obviously that doesn't do so good when the result is not an object.
Changed Database::sourceStream() to send itself as the second parameter to the result-handling callback, so the callback knows which DB to check.