Also made optionset use the value set by optionset. We're not checking
whether the option is set or not, because we would just throw an error
if it wasn't set, and it throws an error anyway.
PHPBB3-10240
Due to the usage of `__DIR__` for the file includes the tests can't
be ran on systems with PHP < 5.3. Replace all occurances of
`__DIR__` with `dirname(__FILE__)`.
PHPBB3-10011
