pkg_add cache for use with -K flag

I have been thinking about adding some simple behavior to deal with
pkg_add of failed or repeated packages.  Currently with pkg_add -r, all
packages (including dependencies) are re-fetched if there is any
failure.  With the -K flag though, the dependent packages should already
be present on the local filesystem and can thus be used instead of the
remote versions.

The patch would be enabled if the PKGDIR environmental variable is
present.  When adding a package, it would first check PKGDIR for the
dependencies and install from local copies if present.  I think the main
package itself would still need to be re-fetched since -r doesn't
specify a version and there is no way to tell if the .tgz in PKGDIR is
the most recent.

Has anyone thought along these lines before?

-- 
Nate