It has been suggested to me that we need a way to have a bulk pkgsrc build
keep certain packages (xpkgwedge in particular) installed during the
entire build.  This should be easy enough to do, but I'd like comments on
this:

Are there any other packages that we'd ever want to handle this way?

If not, its easy enough to special case xpkgwedge.  Perhaps setting
BULK_XPKGWEDGE=YES would trigger the use of xpkgwedge for the entire bulk
build.

If there are other packages we might want to do this too, I guess setting
something like
BULK_PREREQ+=pkgtools/xpkgwedge
BULK_PREREQ+=foo/bar
and I could check for packages in that list and keep them installed.

Comments?

-Dan