[patch] Don't use tree when output is not a terminal

[Paul]

I've written a patch which tests whether the output is a terminal, and
then formats using `tree` only in that case.  If not, `find` is used
instead.  This would simplify scripting around pass.

It may be useful to add `-s|--simple` and `-P|--pretty` parameters to
the find and show commands to override this behavior.

Thoughts? Corrections?

--Paul

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