add missing lib include
open stdin to a tty when not already, for tests

as seen in
http://www.cpantesters.org/cpan/report/be100188-3938-11e4-8a3c-ccfa76850be1

Also accompanied by an author test that runs all tests under these conditions,
just to make sure.
Dist-Zilla-Plugin-PromptIfStale-0.026

          - fix tests (new in 0.025) that fail when stdin is not a tty (e.g.
            piping module names to cpanm)