* test/emacs:
- New subtest "notmuch-show: collapse all messages in thread":
`notmuch-show-open-or-close-all' with prefix arg ("C-u M-RET")
collapses all messages in thread.
- New subtest "notmuch-show: uncollapse all messages in thread":
`notmuch-show-open-or-close-all' without prefix arg ("M-RET")
uncollapses all messages in thread.