Bug (emacs): lexical binding breaks tag hooks

[Matt Lundin <mdl@imapmail.org>]

With the upgrade to notmuch 0.32, functions added to
'notmuch-after-tag-hook' or 'notmuch-before-tag-hook' no longer have
access to the 'tag-changes' or 'query' variables advertised in the
docstrings of both hooks. If I try to access either variable in a hook
function, emacs throws an error. I believe this results from the
addition of lexical binding in commit fc4cda07a9af.

Here are steps to reproduce:

1. Create a hook that accesses either the 'query' or 'tag-changes'
   variable:

(defun my-notmuch-tag-change-test ()
  tag-changes)

(add-hook 'notmuch-before-tag-hook #'my-notmuch-tag-change-test)

2. Attempt to change a tag in a message. This results in the following
   backtrace:

--8<---------------cut here---------------start------------->8---
Debugger entered--Lisp error: (void-variable tag-changes)
  my-notmuch-tag-change-test()
  run-hooks(notmuch-before-tag-hook)
  (progn (run-hooks 'notmuch-before-tag-hook) (if (<= (length query) notmuch-tag-argument-limit) (apply 'notmuch-call-notmuch-process "tag" (append tag-changes (list "--" query))) (let ((batch-op (concat (mapconcat #'notmuch-hex-encode tag-changes " ") " -- " query))) (notmuch-call-notmuch-process :stdin-string batch-op "tag" "--batch"))) (run-hooks 'notmuch-after-tag-hook))
  (if tag-changes (progn (run-hooks 'notmuch-before-tag-hook) (if (<= (length query) notmuch-tag-argument-limit) (apply 'notmuch-call-notmuch-process "tag" (append tag-changes (list "--" query))) (let ((batch-op (concat (mapconcat ... tag-changes " ") " -- " query))) (notmuch-call-notmuch-process :stdin-string batch-op "tag" "--batch"))) (run-hooks 'notmuch-after-tag-hook)))
  notmuch-tag("id:87v981o2hj.fsf@tethera.net" ("+test"))
  notmuch-show-tag(("+test"))
  notmuch-show-add-tag(("+test"))
  funcall-interactively(notmuch-show-add-tag ("+test"))
  call-interactively(notmuch-show-add-tag nil nil)
  command-execute(notmuch-show-add-tag)
--8<---------------cut here---------------end--------------->8---

Best,

Matt