debian build-dependencies for testing should be marked <!nocheck>

[Daniel Kahn Gillmor]

hi notmuch people--

debian/control's build-dependencies list a bunch of things that i think
are only relevant for running the tests (e.g. dtach -- and maybe emacs
and bash-completion and other packages).

These should be marked <!nocheck> so that dpkg-buildpackage can know to
ignore them when trying to build with BUILD_DEB_OPTIONS=nocheck.

This is called a "build profile", if you want to look up more about it:

  https://wiki.debian.org/BuildProfileSpec
  https://bugs.debian.org/757760

I'd send a patch, but i'm not entirely sure which packages are strictly
for the build-time tests, so i hope someone with more experience with
the debian package can mark them appropriately.  Thanks!

Regards,

       --dkg