Create a generic PKGMESSAGE, and use it where appropriate.
Make sure that bsd.port.pre.mk is included before bsd.squirrelmail.mk.
For ports with maintainers, I haven't switched you to the new
PKGMESSAGE, but I have corrected paths in pkg-message.in where
necessary. I also got a little over-zealous in cleaning redundant
definitions from the headers. Apologies in advance if this rubs
you the wrong way.