Use safe string comparisons in SMOF

This subject was brought up in https://github.com/shoestrap/shoestrap/issues/267. 

If any of the variable values are boolean type of TRUE or FALSE, comparing any string to it will return TRUE when using == or !=.

i.e. This returns true in PHP: 
```php 
var_dump((bool) "false");   // bool(true)
```

I don't know if this is absolutely necessary but it's a safe practice, especially for an important class such as the class.options_machine.php. 

Please excuse the indent spacing. Ignore whitespace when doing a comparison.