[Coco] DW4 and external midi devices

[Aaron Wolfe]

I added some midi commands to the 'dw' interface which let you view
available midi devices and switch the output of the /MIDI device to
use any of them.
Using a cheap usb midi adapter connected to a Ensoniq synthesizer,
latency/timing issues seem to be much reduced.  I'm hesitant to say
eliminated, but it's pretty good so far.
You can also use this command to select the midi synth in your sound
card, which probably sounds better than the one built into the Java
VM.

A video of this in action:   http://www.youtube.com/watch?v=g721tj7VnJs

I am not good with making videos (and my cell phone isn't either).
The text on the OS-9 screen was sort of hard to make out.  Here's what
the output from the new midi commands looks like:

{N2|03}/DD:dw midi show

DriveWire MIDI status:

Devices:
[0] In USB Midi 1x1 (MidiInDevice)
    No details available, Unknown vendor 67.0
[1] Microsoft MIDI Mapper (MidiOutDevice)
    Windows MIDI_MAPPER, Unknown vendor 5.0
[2] Microsoft GS Wavetable Synth (MidiOutDevice)
    Internal software synthesizer, Unknown vendor 1.0
[3] Out USB Midi 1x1 (MidiOutDevice)
    External MIDI Port, Unknown vendor 67.0
[4] Real Time Sequencer (RealTimeSequencer)
    Software sequencer, Sun Microsystems Version 1.0
[5] Java Sound Synthesizer (MixerSynth)
    Software wavetable synthesizer and receiver, Sun Microsystems Version 1.0

Current MIDI output device: Java Sound Synthesizer

{N2|03}/DD:dw midi out 3
Set MIDI output device: Out USB Midi 1x1

{N2|03}/DD: