MFC: Merge sendmail 8.14.7 from stable/8

Approved by:	re (delphij)
MFC: Minor changes to force commit these files so new freebsd*.cf files are
     built to use the new sendmail-8.14.7/cf tree.  Merged from stable/8.

Approved by:	re (delphij)
MFC r249525:
Rewrite origin_subst_one() to get rid of the wrong limit on the length
of the resulting string.

MFC r250075:
Properly terminate the result string for intermediate results.

Approved by:	re (jpaetzel)
Update releng/8.4 to -RC3 status.

Approved by:	re (implicit)
Update releng/8.4 branch to -RELEASE status, pending final preparation.

Approved by:	re (implicit)