Merge Down //p4-sdp/r26.1.0 -> main: real integration (p4 merge,
not an independent mirrored edit) of everything that originated
in the release stream today -- the SDP-1394/1395 Emergency Bug
Fixes, the ReadMe.md HMS-link hot fix, and the P4D Version
Compatibility fix in ReleaseNotes.adoc. All code/doc files
resolved with 0 conflicts (differences were only RCS $Id:/$Change:
keyword lines, which correctly self-expanded to main's own
values). Regenerated ReleaseNotes.html/.pdf to pick up the
P4D-compatibility content.