alternative MTAs. Therefore, always install rc.sendmail, regardless of
NO_SENDMAIL make.conf setting. Users can still set mta_start_script to a
different script.
This commit is after a repo-copy of src/etc/sendmail/rc.sendmail to
src/etc/rc.sendmail.
Noticed by: Calvin NG <calvinng@brel.com>
MFC after: 3 days