AltairZ80: Improved Altair Minidisk support from Mike Douglas
ETHER: Fix to allow proper building and operation when networking support is undesired or unavailable. #143
sigma: Fix shutdown/detach issue with tape devices.

Also add makefile and Visual Studio Project definitions to build the incomplete/unsupported sigma and alpha simulators.
VAX: Allow potentially pending console output to be delivered prior to halting back to the sim> prompt
VAX: Added support for the DEQNA device on Ultrix 1.x. Henry Bent observed that the deqna driver in this OS counted on older DEQNA firmware which automatically enabled interrupts after a software reset.

CPU Idle detection for this OS is now supported and the combination of SET CPU IDLE=ULTRIX-1.X and explicitly using a DEQNA device (SET XQ TYPE=DEQNA) will enable the automatic enabling of device interrupt generation.
ETHER: Fix asynch reader thread rundown in error recovery path.
MicroVAX I: Fix to allow reboot when the initial boot didn't specify a boot device (i.e. a sniff boot)
VAX: Make sure that Ultrix 1.X specific behaviors are only in effect with that OS
Compiler suggested cleanups - Johnny Billquist
VAX8600: Fix for console I/O from Johnny Billquist

Writing to the TXCS register always updated the transmit enable mask, even when the "Write Mask Now" bit was not set. That bit needs to be set for the write to the register to actually update the transmit enable mask.