lib: Start all function names in notmuch-private.h with

As noted in devel/STYLE, every private library function should start
with _notmuch. This patch corrects function naming that did not adhere
to this style in lib/notmuch-private.h. In particular, the old function
names that now begin with _notmuch are

    notmuch_sha1_of_file
    notmuch_sha1_of_string
    notmuch_message_file_close
    notmuch_message_file_get_header
    notmuch_message_file_open
    notmuch_message_get_author
    notmuch_message_set_author

Signed-off-by: Charles Celerier <cceleri@cs.stanford.edu>
emacs: Fix indentation.

Fix the indentation of `notmuch-show-mode-map'.
test: make test_emacs call post-command-hook

The unread/read changes will use the post-command-hook. test_emacs
does not call the post-command-hook. This adds a notmuch-test-progn
which takes a list of commands as argument and executes them in turn
but runs the post-command-hook after each one.

The caller can batch operations (ie to stop post-command-hook from
being interleaved) by wrapping the batch of operations inside a progn.

We also explicitly run the post-command-hook before getting the output
from a test; this makes sense as this will be a place the user would
be seeing the information.
emacs: show: add an update seen function to post-command-hook

Add a function for updating seen messages to the
post-command-hook. This function calls a customizable (by eg
defcustom) function with parameters the start and end of the current
window and that function can decide what to mark read based on that
and the current point.

Since this is in the post-command-hook it should get called after most
user actions (exceptions include user resizing the window) so it
should be possible to make sure the seen status gets updated whether
the user uses notmuch commands like next-message or normal emacs
commands like scroll-up.

It removes all of the old mark read/seen points but introduces a
simple example function that just marks the current message read if it
is open. This function has one small subtlety: it makes sure it
doesn't mark the same message read twice (in the same instance of the
same buffer); otherwise the post-command-hook makes it impossible for
a user to manually mark a message unread.

This fixes the current bugs (imo) that closed messages can be marked
read, and that opening a closed message does not mark it read.

Another advantage of using the post-command-hook any programmatic use
with point passing through a message will not mark it read.
devel: news2wiki to recognize yyyy-mm-dd or UNRELEASED as release date

The yyyy-mm-dd (actually \d\d\d\d-\d\d-\d\d) for a bit more restrictive
(and self-documentative) than the \w\w\w\w-... that used to be there and
UNRELEASED so that developers can test the latest NEWS converted to mdwn
format before submitting NEWS patches.
test: redirect gdb output to a file.

It seems that the normal output redirection in the test suite doesn't
work for gdb, but it's nice to have output in a file for debugging.