Bug#352896: apt-get update: the following signatures couldn't be verified

[Allan Lyons <allan@rahab.wycliffe.ca>]

Package: apt
Version: 0.6.43.2

There is an error in the error message when the signature can't be
verified.  This can easily be triggered when running apt-get update when
one of the repositories is signed by a key that is unknown.  The warning
message printed says:

W: You may want to run apt-get update to correct these problems.

However, the proper message should say to run apt-KEY.

It would be nice if this message was fixed since the wrong message can
send a new user on a LONG path when the answer is easy to find if
apt-key was mentioned.