contrib: pick: override notmuch-show-get-prop

We override notmuch-show-get-prop so that many of the show functions
can be used in notmuch-pick without modification. The main use is that
it means notmuch-show-get-message-id `works' in pick. Thus we get all
the stash functions and several other `for free' in pick.
contrib: pick: Link in notmuch-show-pipe-message

Since we can now use show functions directly in pick we can drop pick-pipe-message.
contrib: pick: Link in attachment functions straight from notmuch-show

We can use the attachment functions straight from
notmuch-show. notmuch-show-view-all-mime-parts might be deprecated so
we either want to undeprecate it or not have this binding.
contrib: pick: Link in stash map straight from notmuch-show

These functions all now work straight from their notmuch-show
implementation so link them in.

Stash functionality was one of the key missing things in notmuch-pick.
contrib: pick: add in to-message-window function
contrib: pick: add button press helper

We will want to be able to activate buttons not in the current
buffer (ie in the message pane) so it is helpful to have a way of
activating a button without signalling error if there is no button.
contrib: pick: pass tab through to the message pane

This makes tab move to next button in the message pane and binds
button activate (in message pane) to "e". This means that is easy to
toggle hidden parts or hidden citations etc in the message pane.
contrib: pick: close window function
contrib: pick: make help close the message pane first

Previously pressing "?" for help when the message pane was open meant
the help window was very small. Close the message pane before
displaying help.
contrib: pick: add in binding to view raw message

Note this does rely on the fact that we have over-ridden notmuch-show-get-properties
contrib: pick: use close-message-pane for reply etc

We can save some code duplication by using the new close-message-pane
functionality for reply, forward, and new mail.
notmuch-config: use strchr(), not index() (Solaris support)

notmuch-config.c has the only use of the function named "index()" in the
notmuch source.  Several other places use the equivalent function
"strchr()"; this patch just fixes notmuch-config.c to use strchr()
instead.  (Solaris needs to include <strings.h> to get the prototype for
index(), and notmuch-config.c was failing to include that header, so it
wasn't compiling as-is.)
cli: add --duplicate=N option to notmuch search

Effective with --output=files, output the Nth filename associated with
each message matching the query (N is 1-based). If N is greater than
the number of files associated with the message, don't print anything.
test: test notmuch search --duplicate=N

Add test for notmuch search --duplicate=N option.
man: document notmuch search --duplicate=N

Document the notmuch search --duplicate=N option.
cli: add --output=files option to notmuch count

Add support for querying the total number of files associated with the
messages matching the search. This is mostly useful with an
id:<message-id> query for a single message.
test: test notmuch count --output=files

Add tests for notmuch count --output=files option.
man: document notmuch count --output=files

Document the notmuch count --output=files option.
NEWS: cli options for improved duplicate message handling
man: clarify folder: prefix regarding duplicate files

The results for folder: prefix are a source of recurring confusion.