general ports config question

[Gary Aitken]

I've been wanting gimp 2.8.0 (now 2.8.2) for a bit and as it's been slow to 
show up in the ports collection, thought I would see about building it.
Unfortunately, I don't know squat about the process but figured trying it 
would help slow my brain from atrophying at its currently rapidly accelerating 
pace.

Not wanting to disrupt the current environment (gimp 2.6 built from ports), 
I wanted to build 2.8 someplace else.  
Since gimp-2.8.2 requires babl-0.1.10, I thought I'd start there.

It's not clear to me what params or environment variables to set
prior to running ./configure to generate a Makefile which will cause it to
use newly built stuff in preference, 
but still find installed stuff if necessary
and then install in a different place.

Just doing ./configure and then make craps out with 
  Making all in babl
  "Makefile", line 959: Missing dependency operator
which is a line which says:
  -include $(INTROSPECTION_MAKEFILE)
which is defined empty

Looking at the installed version of babl (babl-0.1.6), 
this and other symbols are all defined to be something out of /usr/local
which leads me to think I'm missing something pretty basic.

hints?

Thanks,

Gary