[RFC] Seeking Approval: include bsd.port.pre.mk so SRC_BASE is defined before referenced

[Mark Linimon]

Unfortunately certain things need to be defined before bsd.port.pre.mk
is included.  So, pointy hat to me for giving bad advice.

These show up immediately as "bad distinfo" problems:

http://pointyhat-west.isc.freebsd.org/errorlogs/amd64-errorlogs/e.10-exp.20120522050031.pointyhat-west/lsof-4.86,7.log
http://pointyhat-west.isc.freebsd.org/errorlogs/amd64-errorlogs/e.10-exp.20120522050031.pointyhat-west/cairo-reference-1.12.2,1.log

I have already fixed lsof, but I don't understand cairo-reference.

mcl