Log Message:
notmuch: update to 0.28.

Notmuch 0.28 (2018-10-12)
=========================

General
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Improve threading

  The threading algorithm has been updated to consider all references,
  not just the heuristically chosen parent (e.g. when that parent is
  not in the database). The heuristic for choosing a parent message
  has also been updated to again consider the In-Reply-To header, if
  it looks sensible. Re-indexing might be needed to take advantage of
  the latter change.

Handle mislabelled Windows-1252 parts

  Messages that contain Windows-1252 are apparently frequently
  mislabelled as ISO 8859-1. Use GMime functionality to apply the
  correct encoding for such messages.

Command Line Interface
----------------------

Support relative database paths

  Database paths (i.e. parameters to `notmuch config set
  database.path`) without a leading `/` are now interpreted relative
  to $HOME of the invoking user.

Emacs
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Improve stderr handling

  Add a real sentinel process to clean up stderr buffer. This is
  needed on e.g. macOS.

Call `notmuch-mua-send-hook` hooks when sending a message

  This hook was documented, but not functional for a very long time.

Completion
----------

The zsh completion has been updated to cover most of the notmuch
CLI. Internally it uses regexp searching, so needs at least Notmuch
0.24.

Build System
------------

The build system now installs notmuch-mutt and notmuch-emacs-mua with
absolute shebangs, following the conventions of most Linux
distributions.

Test Suite
----------

Fix certain tests that were failing with GMime 2.6. Users are reminded
that support for versions of GMime before 3.0.3 has been deprecated
since Notmuch 0.25.