Fix GPGME signature zero timestamp and locale awareness issues. (closes #3882)

Fix GPGME signature zero timestamp and locale awareness issues. (closes #3882)

GPGME signature information has two minor problems.

[-- Begin signature information --]
*BAD* signature from: Name <user@example.com>
                 aka: Name <user@example.org>
             created: Thu Jan  1 09:00:00 1970
[-- End signature information --]

First, the created timestamp is incorrect when the message is not
verified successfully.

Second, as the code itself has some "TODO" comments, "aka" and
"created" lines are not properly-aligned when LC_MESSAGES != English.