Determining which port installed a build dependency

[Randy Pratt]

Is there a way to determine which port installed a build dependency?

I was using pkg_cutleaves to weed out some unused ports but I'd
prefer not to remove build dependencies if at all possible.  Here is 
an example of a build dependency which is not a run dependency:

	% cd /usr/ports/net/cvsup

	% make build-depends-list
	/usr/ports/lang/ezm3
	/usr/ports/x11/XFree86-4-libraries

	% make run-depends-list
	/usr/ports/x11/XFree86-4-libraries

It is installed:

	% pkg_info | grep ezm3
	ezm3-1.1_1          Easier, more portable Modula-3 ...

If I try to find which port was responsible for installing ezm3 
I get no results:

	% pkg_info -R ezm3-1.1_1
	Information for ezm3-1.1_1:

	%

Is there some slick method for finding this information?  I'd prefer
to keep the build dependencies for the next portupgrade.

The pkg_info(1) man page doesn't make it clear that the -R option
only works for run dependencies.  

Searching with google didn't turn up any useful results either.

Thanks,

Randy