HEADS UP: Recompile milters after sendmail 8.14 upgrade

[Gregory Shapiro]

> Unfortunately, this problem (the need to recompile filters) was found
> after the MFC.  The release engineering team has asked for this notice
> instead of doing a full backout of sendmail 8.14 in the RELENG_[456]
> branches.

Note that I have some new code, currently under review, that eliminates
the need to recompile filters by removing fixing the ABI change.  I will
post another HEADS UP when that change is committed (first to HEAD, then
to the RELENG_[456] branches).  In the mean time, you may want to delay
upgrades until the new code is in place.