Mention lein test takes file args

[ci skip]
Merge pull request #1072 from cldwalker/news-test

Mention lein test takes file args in NEWS
Add GPG doc.
Link the GPG doc to 'help gpg'
Add notice about 'help gpg' to error output.

This covers artifact signing, credential decryption, and dependency
verification.
Remove unneeded bindings around consolidated gpg.
Bugfix: Restrict repo credential lookup to known keys.

The last test in that set is a regression test discovered while working
on #949.
Merge pull request #1074 from timmc/master

Bugfix: Restrict repo credential lookup to known keys.
credentials-fn != credentials