PDP11/VAX: Fix VH device to properly be displayed when the number of lines changes and to avoid problems in debug mode.
PDP11/VAX: Improved debug information to identify the distinct DMC line when multiple lines are in use and added detailed debug output for DDCMP state machine changes.
SCP: Added detailed help (including switches) for SET DEBUG command and an auto flush of the debug output when instruction execution stops.
VAX,PDP11: Fix behavior of simulator when multiple DMC devices are in use concurrently.  Fix for issue #51.

The interrupt acknowledgment logic for the transmit interrupt inadvertently cleared the device interrupt pending flag even when other devices potentially had pending interrupts.

Added line specific indications in the debug output for packet trace debugging.
PDP8: Add device buffer flush capability and keep track of data written state in the device buffer.  Fixes #87
erge branch 'master' of https://github.com/simh/simh