[PATCH v3] emacs: display tags in notmuch-show with links

[Damien Cassou]

This patch obsoletes:
id:1353266322-20318-1-git-send-email-damien.cassou at gmail.com

[PATCH 1/4] emacs: Add a thread's tags to notmuch-show header-line
[PATCH 2/4] emacs: Make tags in notmuch-show header-line clickable
[PATCH 3/4] emacs: Make all tags in `notmuch-show' clickable
[PATCH 4/4] emacs: Add unit-tests for clickable tags

This patch makes clickable all tags that appear in notmuch-show
buffers. Each tag is a link to open a new notmuch-search buffer for
this tag. Additionally, the buffer's header-line now shows the
thread's tags (clickable only if the `header-button' library is loaded
or loadable).

This patch is the first one of an upcoming series whose goal is to
integrate notmuch-labeler into notmuch. See the following for more
details:
https://github.com/DamienCassou/notmuch-labeler

With respect to v2, I took care of the comments you made:
- moved notmuch-tagger-separate-elems to notmuch-lib
- renamed a few methods
- changed some comments to better reflect the method behavior
- changed links in the body so that TAB won't stop at them
- changed miscellaneous small things