[BUG] test suite broken with GETTEXT_POISON=YesPlease

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.