Log Message:
Updated notmuch to 0.23.4.

Notmuch 0.23.4 (2016-12-24)
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Command Line Interface
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Improve error handling in notmuch insert

  Database lock errors no longer prevent message file delivery to the
  filesystem.  Certain errors during `notmuch insert` most likely to
  be temporary return EX_TEMPFAIL.

Emacs
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Restore autoload cookie for notmuch-search.