Pass $opts by reference to subscribers of 'SpecialSearchPowerBox' hook to allow them...

Pass $opts by reference to subscribers of 'SpecialSearchPowerBox' hook to allow them to modify it

wikiHow added a new hook called 'SpecialSearchPowerBoxOpts', which was passed only &$opts, so that the Finner extension can unset the $opts array. Enhancing the pre-existing hook is a better solution in this case.

Change-Id: I091cbdc78fc779144554d8420a95435b7048c407