stow-2.1.1 needs a perl module

On about 25 flavors of Unix here in our test lab, builds of stow-2.1.1
all failed.  I tracked down the problem to a perl module that is
needed, but had never been installed on any of our systems:
Test::Output.  Once that module was installed, validation tests and
installations have gone smoothly.

Given that other sites are likely to be missing that module too, I
think that the stow configure script should check for its
availability, and terminate early if it is not found.

As an aside, a good friend of mine is the co-author of an article on
stow and depot that appeared a decade ago in the LISA 2001
proceedings, and I read it again over the weekend.  The authors of
that paper lay out a plan for a future merger of rpm + depot/stow
capabilities to support networked as well as standalone systems.  As
far as I know, nothing has happened to further that goal, but it might
be useful fodder for future GNU stow development.  Here is a pointer
to the paper:

	R. P. C. Rodgers and Ziying Sherwin

	A Management System for Network-Sharable Locally Installed
	Software: Merging RPM and the Depot Scheme Under Solaris

	Proceedings of LISA 2001: 15th Systems Administration
	Conference, December 2--7, 2001, Town and Country Resort
	Hotel, San Diego, CA

	ISBN 1-880446-05-7

	http://db.usenix.org/publications/library/proceedings/lisa2001/tech/rodgers.html

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