I find that git-buildpackage seems to clear the environment in some
cases where dpkg-buildpackage does not.
This results in a problem for some workflows that include the use of
GnuPG when a gpg-agent is running with a different environment than the
the spot where i've noticed it is:
* have a gpg-agent set up with no DBUS_SESSION_BUS_ADDRESS environment
variable of its own
* use pinentry-gnome3 as the default pinentry
* build a package with "gbp buildpackage"
* have gnupg2 2.1.x instealled
When it comes to the step to sign the .dsc and .changes files, i get a
signature failure with no prompts.
If i use "dpkg-buildpackage" instead, i get a gnome3-based pinentry
prompt and the files get signed.
And if i kill the gpg-agent and restart it with the same socket and a
default dbus environment variable that works with the current session
 then even "gpb buildpackage" will work and have signing happen.
So this makes me think that gpb is stripping the environment before
invoking gpg, but i havne't been able to track it down.
 restarting the agent from within a running X11 session goes like
gpg-connect-agent killagent /bye && gpg-connect-agent /bye
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