Merge branch 'js/gpg-errors'

Error messages given upon a signature verification failure used to
discard the errors from underlying gpg program, which has been
corrected.

* js/gpg-errors:
  gpg: do show gpg's error message upon failure
  t7510: add a test case that does not need gpg

diff --cc gpg-interface.c
Simple merge

diff --cc t/t7510-signed-commit.sh
Simple merge