Compiler indicated cleanups to Fix #105
PDP10: Added display support of PC value in debug messages.
TMXR: Added support to reasonably set modem bits when a line has dedicated listen port defined or uses datagram transport.
SCP: Add SHOW -C BREAK to display the currently defined breakpoints as commands which can be used to redefine them later.

Note: This excludes the possibility of there being a -C breakpoint type.  Since there are potentially 26 different breakpoint types, this exclusion is not likely to have a significant impact.
VAX,PDP11,PDP10: Added explicit support to enable (or disable) DMR Micro Diagnostics which corresponds to the SW10 hardware switch.

Also, always process initialization commands without regard to whether the DMC/DMR line is attached and return diag error status if the line isn't attached.
PDP8: Add new breakpoint command based on instruction value (Opcode) (from Dave Gesswein) as discussed in issue #75
Compiler indicated cleanups
PDP11,PDP18B: Add device buffer flush capability and keep track of data written state in the device buffer.  These are cousin bugs described in issue #87
PDP8: Binary loader can now read multiple section tapes.  Fix from Dave Gesswein to issue #74.
Merge branch 'master' of https://github.com/simh/simh