Replace the use of ini_set() with set_include_path()

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Giving that ini_set() is a dangerous function to have enabled on shared hosting and many hosts disable this function. I think concrete5 shouldn't depend on it heavily as it currently does.

In the file base.php where ini_set() is used to define libraries paths, set_include_path() will work on all servers, hence should be use at least in this case instead ini_set().