Important change to the NVR code to "fix" the PS/1 and PS/2 systems, plus a cleanup.
All device tables now end with a NULL, not an empty string.
Configuration code now deals better with this.
Machine and Video lookup now return -1 if not found/available, and pc_init() will throw the user into Setup if that is the case.
If for some reason the configured memory size exceeds machine limit, it is now adjusted.
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.
Changes to the memory manager reduced by 120MB for machines with CPU < 80386.
Changes to the 86F diskette data processor (required by all floppy controllers) reduced by 330M.
Test machine OpenXT now runs at 240MB, instead of 680MB.
