
Sound_InstallVoice
------------------

Entry:  R0 -> voice generator to install
        R1 = voice slot to install in (or 0 for first empty slot)
Exit:   R0 -> name of previous voice
        R1 = voice number allocated (or 0 for fail)

Entry:  R0 = 0
        R1 = slot number to interrogate
Exit:   R0 -> name of voice
        R1 = (preserved)

New flavours
------------
Entry:  R0 = 1
        R1 = voice slot to install in (or 0 for first empty slot)
        R2 -> voice generator to install
        R3 -> voice name in local language (data is copied so can vanish
              as soon as the SWI has returned) or 0 for no local name
Exit:   R0 = (preserved)
        R1 = voice number allocated (or 0 for fail)
        R2 -> name of previous voice
        R3 = (preserved)

Entry:  R0 = 2
        R1 = slot number to interrogate
Exit:   R0 = (preserved)
        R1 = (preserved)
        R2 -> name of voice
        R3 -> name of voice in local language (gaurunteed none zero and
              valid if R2 is none zero)

Entry:  R0 = 3
        R1 = voice slot to change local name of (0 not allowed)
        R2 = 0 (this is required)
        R3 -> new voice name in local language, replaces any peviously
              specified or gives it a local name if none exists.
Exit:   R0 = (preserved)
        R1 = (preserved)
        R2 = (preserved)
        R3 = (preserved)
