PDP10, PDP11, VAX: Make sure that the DMC and DUP devices produce the right messages when an attach is attempted to an already attached line
SDS: Add assembly/disassembly support for common SYSPOPs.

Add new instruction class -- I_V_SPP for SYSPOPs and definitions for the standard ones provided by the time sharing system. Add instruction name annotation to the opc_val array.
SDS: Clean up CPU modes and record CPU mode in instruction history record

The three CPU modes -- normal, monitor and user were represented by two binary flags (nml_mode and usr_mode). The code is simpler and easier to read if the three modes are represented by one three-valued variable, cpu_mode. In addition, record the CPU mode in the instruction history record, and add the mode to the history display.

In addition, add an optional flag to the SET CPU HISTORY=n command to *not* record instructions executed in a particular CPU mode.  Flags are -n, -m and -u for normal, monitor and user mode respectively.  For example, SET -m CPU HISTORY=n will only record instructions executed in normal or user mode, and will not record instructions executed in monitor mode. This change aids user-mode program debugging by not filling the history with monitor-mode service functions and interrupt activity.
SDS: Documentation change for new history and SYSPOP features.
Merge git://github.com/simh/simh
PDP10: Added DMA transfer debugging (IN, OUT and NXM) to the unibus adapter.
PDP10: Fix formatting of UBA DMA debug output
PDP10: Extended UBA DMA debug output to also be available when doing DMA in 16bit or 18bit modes and added display of words and bytes to the debug output.
Compiler suggested cleanup