debian: re-enable atomicity test on arm64

according to

   https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=757454

the kernel problem which caused this test to fail should be
fixed now
test/emacs: globally force the html renderer to html2text

Previously we did this for a single test, but some other proposed
tests ( id:1398105468-14317-3-git-send-email-amdragon@mit.edu ) show
similar breakage when switching renderers.
emacs: Remove redundant NTH argument from `notmuch-get-bodypart-content'.

This can be derived from the PART argument (which is arguably
canonical), so there's no sense in giving the caller an extra foot
gun.
test: New tests for Emacs charset handling

The test of viewing 8bit messages is known-broken.  The rest pass, but
for very fragile reasons.  The next several commits will fix the
known-broken test and make our charset handling robust.
emacs: Fix coding system in `notmuch-show-view-raw-message'

This fixes the known-broken test of viewing 8bit messages added by the
previous commit.
python: Add binding for notmuch_query_add_tag_exclude

Implemented as the method `exclude_tag` of the class `Query`. This method takes
one argument, a string containing the name of the tag to exclude.
emacs: jump: fix compile warning on emacs 23

notmuch-jump uses window-body-width which is not defined in emacs
23. To get around this it does

(unless (fboundp 'window-body-width)
  ;; Compatibility for Emacs pre-24
  (defalias 'window-body-width 'window-width))

This makes sure window-body-width is defined and all should be
well. But it seems that the byte compiler does not realise that this
guarantees that window-body-width will be defined and so, when
compiling with emacs 23, it gives an error

In end of data:
notmuch-jump.el:172:1:Warning: the function `window-body-width' is not known to be defined.

Domo and I came to following on irc: wrap the (unless (fboundp ...))
inside eval-and-compile which ensures that both the test and the
defalias (if needed) happen at both compile and load time.  This fixes
the warning.
lib: actually return failures from notmuch_message_tags_to_maildir_flags

The function takes great care to preserve the first error status it
encounters, yet fails to return that status to the caller. Fix it.
cli/insert: rename check_folder_name to is_valid_folder_name

An "is something" predicate conveys the meaning better. While at it,
improve the function documentation and error message. Besides the
error message change, no functional changes.
cli/insert: move add_file_to_database to a better place

Move add_file_to_database around to keep the filesystem related
functions grouped together, improving readability. No functional
changes.
cli/insert: rename file copy function

The copying has nothing to do with stdin, so call it copy_fd
instead. While at it, improve documentation and reverse the
parameters, as destination is traditionally the first parameter.
cli/insert: clean up sync_dir

Clarify the code slightly, improve error messages. Apart from the
error message changes, no functional changes.
cli/insert: use a single recursive mkdir function

Combine make_directory() and make_directory_and_parents() into a
single recursive mkdir_recursive() function. Clarify the code and
improve error handling. Improve error messages. Switch to using the
new function in maildir_create_folder(). Constify talloc context.
cli/insert: abstract temporary filename generation

This will clean up the usage. There's the slight functional change of
potentially ending up doing extra gethostname and getpid calls, but
this is neglible.
cli/insert: rehash file writing functions

Make the function calls make more sense as independent building blocks
of the big picture, with clear inputs and outputs. Split up
write_message into two. Improve function documentation. Cleanup and
clarify the error paths.