Always search for the full package name in existing IMPORT-FROMs

[tdrhq]

.. As opposed to just looking at prefixes. Previously, If you had an existing defpackage like this:

(defpakage :foo
(:import-from :bar/car
:find)))

And you imported bar::position, you'll end up with something ugly like this:

(defpackage :foo
(:import-from :bar
:position/car
:find))

[tdrhq]

This is a pretty common occurrence if you use single-package-per-file style, since packages have a hierarchical structure to them.

(PS. My next PR will be a bit more interesting, and you might like it. I have some patches locally where I can do C-c C-i on an symbol without the package specified, and it shows you a list of options in ido-mode to pick from. It greatly simplifies life, and I'll try sending another PR with that feature once this PR goes in.)