[BUG] test suite broken with GETTEXT_POISON=YesPlease

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

As a refresh of everyone's memory (because mine needed it). This is a
feature I added back in 2011 when the i18n support was initially
added.

There was concern at the time that we would inadvertently mark
plumbing messages for translation, particularly something in a shared
code path, and this was a way to hopefully smoke out those issues with
the test suite.

However compiling with it breaks a couple of dozen tests, I stopped
digging when I saw some broke back in 2014.

What should be done about this? I think if we're going to keep them
they need to be run regularly by something like Travis (Lars CC'd),
however empirical evidence suggests that not running them is just fine
too, so should we just remove support for this test mode?

I don't care, but I can come up with the patch either way, but would
only be motivated to write the one-time fix for it if some CI system
is actually running them regularly, otherwise they'll just be subject
to bitrotting again.