[exim-dev] Patches and stuff

I've been on a catch-up bing, merging fixes. I was on a plane for a
chunk of it, and working on MacOS, where I believe the test suite
doesn't run (case-insensitive FS), so have skimped on that.

Current plan is to finish the patch stream, test docs build and tests
pass, fix up any changes then.

So there's a smallish risk of HEAD being not-as-stable-as-it-should-be
right now.

-Phil