- Prevent buildworld from trying to write to /etc/mail/

- Prevent buildworld from trying to write to /etc/mail/
- Stop 'make clean' from removing SENDMAIL_CF
- install and distribute targets should not attempt to build anything
- SENDMAIL_ADDITIONAL_CF were not installed in the distribution case
- If SENDMAIL_SET_USER_ID was defined, submit.cf was needlessly installed
  in the distribution case
- Collapse install and distribution target into one to remove code
  duplication

Submitted by:	ru
MFC after:	5 days