apachesolr_do_query() has to take &$params by reference

The way a search runs now, we call apachesolr_search_execute(), which calls apachesolr_do_query(), and then apachesolr_search_process_response(). Both of those functions take $params as an argument, but apachesolr_do_query has all of the alters() and modifies() and finalizes(), and it is a common case that $params is a different beast by the time apachesolr_search_process_response() comes about. Yet having the right $params is crucial to apachesolr_search_process_response() being able to do its job correctly. Thus, the easiest solution for the time being, without refactoring the whole search flow, is to make &$params a reference into apachesolr_do_query().