Make the "uninit variable" warning to say "concat or string"

Make the "uninit variable" warning to say "concat or string"
or "join or string" when in concat or join .

Subject: Re: [ID 20000403.009] uninitialised concatenation???
From: "M.J.T. Guy" <mjtg@cus.cam.ac.uk>
Date: Tue, 04 Apr 2000 18:22:58 +0100
Message-Id: <E12cX2Y-000364-00@taurus.cus.cam.ac.uk>

Subject: [ID 20000330.052] Use of uninitialized value in concatenation (.)
From: William R Ward <hermit@BayView.COM>
Date: Thu, 30 Mar 2000 19:50:03 -0800
Message-Id: <200003310350.TAA13319@komodo.bayview.com>

p4raw-id: //depot/perl@6434