Log Message:
Updated notmuch to 0.23.1.

Notmuch 0.23.1 (2016-10-23)
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General
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Require Xapian >= 1.2.6

  The ifdef branch for older Xapian (pre-compact API) had bit-rotted.

Emacs
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Fix default colours for unread and flagged messages

  In 0.23 the default colours for unread and flagged messages in
  search view were accidentally swapped. This release returns them to
  the original colours.

  A related change in 0.23 broke the customize widget for
  notmuch-search-line-faces. This is now fixed.

Fix test failure with Emacs 25.1

  A previously undiscovered jit-lock related bug was exposed by Emacs
  25, causing a notmuch-show mode test to fail. This release fixes the
  bug, and hence the test.