Made (o) more robust.

Calling 'commands - secondary (o)' now reveals ALL commands available at a
menu.

Example:

    Score manager - active scores

        1: Betörung (2012)
        2: Čáry (2006)
        3: L'archipel du corps (2011)
        4: L'imaginare (2010)
        5: Lidércfény (2008)
        6: Mon seul désir (2009)
        7: Poème récursif (2005)
        8: Red Shift Hijinks (2005)
        9: Sekka (2007)
        10: Traiettorie inargentate (2013)

        scores - new (new)

        library - manage materials (lmm)
        library - manage stylesheets (lmy)

        scores - show all (ssl)
        scores - show active (ssv)
        scores - show examples (ssx)
        scores - show mothballed (ssmb)
        scores - show user (ssu)

        cache - view (cv)
        cache - write (cw)

        back - go (b)
        home - go (h)
        score - go (s)

        commands - hidden (n)
        commands - secondary (o)

        LilyPond - view log (lvl)

        Python - doctest (pyd)
        Python - interact (pyi)
        Python - test (pyt)

        repository - add (radd)
        repository - commit (rci)
        repository - status (rst)
        repository - update (rup)

        scores - tour next (stn)
        scores - tour prev (stp)

        session - display variables (sdv)

        source code - edit (sce)
        source code - location (scl)
        source code - track (sct)

        system - quit (q)

    > q