Don't declare class if they already exist

[bfintal]

This is to prevent PHP errors when scssphp is used multiple times.

Use case: I'm using scssphp in a WordPress plugin and if another plugin also uses scssphp, this results in errors

[varunsridharan]

i too used this is in WP Plugin.. i was search for it..
+1 👍

[robocoder]

Understood but the PR doesn't work as intended, for example:

<?php
include_once 'path1/scssphp/scss.inc.php';
include_once 'path2/scssphp/scss.inc.php';

I'll fix this in the develop branch.