- include saved option only if the port is OPTIONS aware (defines OPTIONS)
- The options a saved if:
- ${OPTIONSFILE} if that is defined
- ${PORT_DBDIR}/${UNIQUENAME}/options if UNIQUENAME is defined
- ${PORT_DBDIR}/${LATEST_LINK}/options
  if UNIQUENAME is undefined and LATEST_LINK is defined
- ${PORT_DBDIR}/${PKGNAMEPREFIX}${PORTNAME}/options
  if UNIQUENAME and LATEST_LINK are undefined

This requires PKGNAMEPREFIX, UNIQUENAME and LATEST_LINK to be defined
*before* including bsd.port.pre.mk.

This patch tries to guard against errors by evaluating OPTIONSFILE early
and checking if this value does not change.

*ALL* -client/-server ports have to define LATEST_LINK or UNIQUENAME if
the client and server ports require different saved options.

- bring the ===> messages in line with the existing ones by using PKGNAME
  instead of PORTNAME
- the same for the dialog title
- use ECHO_CMD instead of ECHO_MSG to write the OPTIONSFILE comment,
  add a line with the PKGNAME
- issue a note during compiling that user-specified options have been found
- make the output of the showconfig target a little more user friendly, even
  though unformatted.