Build and test ruby bindings

[David Bremner]

This series collects some patches that were originally part of the
"count API change" series, and adds a few fixups that are designed to
help with building in MacOS and other non-Gnu places (although they
haven't been tested there yet).

[PATCH 1/5] build: integrate building ruby bindings into notmuch

- obsoletes id:1419971380-10307-2-git-send-email-david at tethera.net

[PATCH 2/5] build/ruby: make use of -Wl,--no-undefined configurable
[PATCH 4/5] build/ruby: use notmuch configure script values for

- These two obsolete (I think)

  id:1416170906-23415-1-git-send-email-ll-notmuchmail at lange.nom.fr

[PATCH 5/5] test: add initial ruby tests

This obsoletes id:1419971380-10307-4-git-send-email-david at tethera.net