SCP: Added hierarchical help capability (from Timothe Litt)
PDP11/VAX: Detect vector conflicts, SHOW IOSPACE and SHOW DEVICE improvements

From Timothe Litt:
  - Detect vector conflicts, SHOW IOSPACE
  - Detect conflicting vector assignments.
  - Correct show iospace display of high vector for multi-unit devices
  - Display vectors in DEV_RDX in show iospace
  - Ignore disabled devices when searching for conflict.
  - Improve device conflict reporting, Report both devices when address conflict is detected.

From Mark Pizzolato:
  - Added optional alternate radix output display for device address and vector values
    displayed by SHOW DEVICE.
    -H and -O switches select hex or octal output in addition to the default radix displayed
    by the normal simulator.
H316: Resurrecting the ARPAnet IMP (from Bob Armstrong)

This summer a group of us worked together to resurrect the original ARPAnet IMP software, and I’m now happy to say that the IMP lives again in simulation.    It’s possible to run the original IMP software on a modified version of the H316 simh and to set up a virtual network of simulated IMPs talking to each other.   IMP to IMP connections, which would have originally been carried over leased telephone lines, are tunneled over IP.  As far as we can tell, everything works pretty much as it did in the early 1970s.  IMPs are able to exchange routing information, console to console communications, network statistics, and they would carry host traffic if there were hosts on the network.  The hooks are in there to allow simh to support the IMP side of the 1822 host interface, and the next step would be to recover the OS for an ARPAnet era host and then extend the corresponding simulator to talk to the IMP simulation.
H316: Added IMP Listing file (from Bob Armstrong)
TMXR: Added option to use UDP transport for packet transport
Merge branch 'master' of github.com:simh/simh
PDP10,PDP11,VAX: Addition of inter operable DUP11, DMC11 and KDP11 devices

This is the results of external KDP development activities.  The KDP side done by Timothe Litt and DMC and DUP by Mark Pizzolato

Additionally, other PDP10 updates from Timothe Litt
SCP/SOCKET: Apply default host more reasonably when parsing host:port strings
TMXR: Tolerate situations where independent devices are bound to different lines of a multi-line MUX.
H316: Rewrote h316_udp to use TMXR lines for UDP transport of data.  Changed h316_mi to leverage built-in loopback mode in TMXR.

This gives UDP transport on all simh host platforms.
TMXR: Support loopback when using packet APIs even if a connection is not active
TMXR: Added loopback support for datagram configured lines to pass full packets in loopback mode.
H316: Added support for proper max data packet size transmission and reception in h316_udp.c
H316: Fix compiler warning
MAKEFILE: Give more clear information when issuing missing libSDL library to enable video capabilities #90
H316: Added "SET dev LOCALLOOP" and "SET dev NOLOCALLOOP" commands to the IMP modem device so that loopback mode can be changed by commands instead of just programatically.
H316: Move the SMK/OTK to h316_cpu (where it belongs!) and Allow the CLK device to be disabled (from Bob Armstrong)
TMXR: Correct const attributes for packet reading APIs.
H316: Improve IMP error recovery when a remote host is restarted.
H316: Updated H316 and IMP documentation and addition of IMP modem loopback functionality and testing (from Bob Armstrong)