Update the style of module_qual.m.

compiler/module_qual.m:
    Change predicates that do case analysis on an input argument
    from having one clause per function symbol to an explicit disjunction.
    (We don't have to worry about indexing in NU-Prolog anymore.)
    This sometimes allows factoring out repeated code.

    Separate the task of module qualifying one thing and the task of
    module qualifying a list of those things.

    Add a distinguishing prefix to the fields of mq_info.