field processor features, merged series

[David Bremner]

This series merges and obsoletes

     id:1458437904-17677-1-git-send-email-david at tethera.net

and all except the last patch

    id:1458437904-17677-1-git-send-email-david at tethera.net

I represents an alternative initial motivation for the library config patches

The first 4 are independent, and provide date:foo queries without the trailing ..

 [PATCH 01/13] config: autodetect xapian-1.3
 [PATCH 02/13] configure: detect Xapian:FieldProcessor
 [PATCH 03/13] lib: optionally support single argument date: queries
 [PATCH 04/13] lib/cli: add library API / CLI for compile time options

This is just an optional cleanup, here to avoid conflicts.

 [PATCH 05/13] configure: check directly for xapian compaction API

This is the previous library config series, rebased. This could be
merged without the following 3, although the motivation is maybe a bit
unclear.

 [PATCH 06/13] lib: provide config API
 [PATCH 07/13] lib: config list iterators
 [PATCH 08/13] CLI: add print_status_database
 [PATCH 09/13] CLI: add optional config data to dump output.
 [PATCH 10/13] CLI: optionally restore config data.

Finally, add support for "named queries". I'm open to suggestions
about naming ("the hardest problem...") but I thought it was a bit
less confusing than "saved searches".

 [PATCH 11/13] CLI: add notmuch-config support for named queries
 [PATCH 12/13] lib: make a global constant for query parser flags
 [PATCH 13/13] lib: add support for named queries

Outstanding issues that I know about

 - missing docs for named queries. It might be nice to have optionally
   included sections in the docs. Or we could just write in something
   like "These search terms are only available if you have field
   processors. `notmuch config get option.field_processor` to find
   out.

- compiler warnings about visibility. I suspect I'm somehow failing at
  C++ here

- compiler warnings about deprecated compact API. This is only related
  in the sense that it is triggered by using xapian 1.3

- as I write this, I realise I probably need to test these patches
  again with xapian 1.2