[PATCH] travis: use ppa:notmuch/notmuch

[David Bremner]

Daniel Kahn Gillmor <dkg at fifthhorseman.net> writes:

> https://launchpad.net/~notmuch/+archive/ubuntu/notmuch/+packages
> contains backports of gmime and gpgme and related cryptographic tools
> to ubuntu xenial.
>
> I tried to do a simple backport of gmime alone, and it failed due to
> the older gpgme in xenial, so this setup resolves those problems.

Whoa, thanks, that looks like a non-trivial amount of work

> This should allow us to continue to use the Travis continuous
> integration build on the release branch.

And on master as well, I guess.

Apropos CI, I'm continuing to look at gitlab CI. I'm currently blocked
by what seems to be a bad interaction between emacs and docker [1].

[1] https://debbugs.gnu.org/cgi/bugreport.cgi?bug=+35557