cleartext indexing, revision 6

[Daniel Kahn Gillmor]

This is the 6th revision of the cleartext indexing series.

It differs from the 5th mainly in minor edits: fixing typos and
improving comments, documentation, and commit messages.  It also has
the following (slightly more) significant changes:

 * improvement of the test suite to permit passing --long-arguments to
   "notmuch new" is now a separate patch (see 11/14 here)

 * only the "index.try_decrypt" config setting is stored in the
   database, as an attempt to (partially) address the concerns raised
   by bremner in id:878tgdy53g.fsf at tethera.net

 * I've introduced a new man page, notmuch-properties(7), as a place
   to collect and reflect on how properties are used within notmuch.
   Hopefully this central place for property documentation will make
   it easier to coordinate conventions and standards used in the
   project in the future.

This series should be applied on top of my two-part trivial
documentation cleanup series starting at
id:20171017165721.1244-1-dkg at fifthhorseman.net

I welcome review and feedback.

Regards,

        --dkg

Series History
--------------

the first version of this series was sent starting at:

id:20170912230153.4175-1-dkg at fifthhorseman.net

version 2 of this series was sent as:

id:20170915055359.24123-1-dkg at fifthhorseman.net

version 3 of this series was sent as:

id:20171010054916.23925-1-dkg at fifthhorseman.net

and version 4 was only partially sent to the list.

version 5 was sent as:

id:20171015064807.14205-1-dkg at fifthhorseman.net