Tandy PSSJ sound driver moved into Tandy machine file.
Fixed the dev_branch devices to use the UNSTABLE flag.
Added Unstable Device warning message in device.c.
Converted AT NVR to be a device, so it gets auto-closed.
Added new machine_close() function which calls optional machine-custom close, updated machine table.
Small fixes here and there.
Re-wored the CDROM code to have a 'speeds' table instead of ugly hard-coding.
