Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Kill the remnants of BOG.

Eliminate ``number register `.U' not defined'' groff(1) warnings.

Update to include a link to the referenced papers when PRINTERDEVICE=html

PR: docs/22140
Submitted by: Cyrille Lefevre <clefevre@citeweb.net>

The rest of the changes needed to support the new version of sendmail (8.11.0).
Beyond changes to the build system, this includes fixing up the sample
freebsd.mc configuration for changes in defaults and syntax, removing
outdated documentation, and updating the release notes.

Make everything work with new bsd.doc.mk and without symlinks in the
source tree. Eliminate papers which require -me macros, 'cos they
currently don't work with groff.