ETHER: Fix bpf filter generation to not generate an invalid filter if only multicast addresses were provided
SCP: Added a mechanism to allow debugging output to display PC values for simulators which don't have a simple register which contains the PC value.
PDP11: XQ Device is now bootable on a Qbus PDP11 simulator.  The ROM based Citizenship tests now pass.

Separate boot ROMs are available for each of the DEQNA, DELQA and DELQA-T devices being simulated.
DEQNA-Lock mode has been added to the DELQA and DELQA-T simulations.
SCP: Show device options can be more flexibly formatted and optionally not display anything.
PDP11: Added support for PC values to be displayed in debug output.

This required a simulator specific implementation since the PDP11 PC register isn't stored in a normal memory location.  It is loaded from a temporary location upon simulator instruction execution startup (and saved to that location when instuction execution stops).  In order to reference the PC value while executing instructions (for debug output), this extended access model is required.
Merge remote-tracking branch 'simh/master'