set_include_path overrides existing include_path

Using Yeloni Exit Popup version 6.3.0.

yetience-plugin.php and wordpress/yetience-class.php both call set_include_path() that overrides the existing include_path. This is breaking my site. Another plugin calls set_include_path() correctly and relies on the setting. When Yeloni Exit Popup resets include_path it breaks that plugin.

I changed it to use an example from the PHP docs where the new include path is appended to the existing include_path (http://php.net/manual/en/function.set-include-path.php – see example #2).

Here is a diff of the two changes:
https://pastebin.com/1wJLxpmk