FreeBSD Support Patches

[Mike Kelly]

Hi,

These patches add some changes necessary for a clean build on FreeBSD,
and for most of the tests to pass.

Also mixed in are a few patches to disable emacs tests when you don't
have emacs, along with tests that depend upon emacs. I could split those
off onto a separate branch if required.

You can find the latest version of these patches on my github repo's
fbsd-support branch:

  https://github.com/pioto/notmuch/compare/master...fbsd-support