How do I tell pkgsrc to install from packages/All instead of rebuilding?

[Michael Huff <mphuff%gmail.com@localhost>]

Hi, all

The question is in the subject. It's very annoying to build a set of 
packages and then when I have to rebuild something new (on a new 
install) the old packages are rebuilt even though they're sitting in 
packages/All.

Basically the behavior I want is that when I go to build a new package, 
pkgsrc checks to see if it's dependencies are installed, if they're not 
installed are they in packages/All and only if the package doesn't exist 
then rebuild; otherwise su pkg_add packages/All/<whatever the dependency 
is>.

I'm assuming that there's a knob somewhere I simply haven't known to 
turn, a setting to specify. I'd appreciate being pointed in the right 
direction.

Thanks!