emacs: breakout notmuch-show-advance functionality from notmuch-show-advance-and-archive
This patch breaks out much of the functionality of
notmuch-show-advance-and-archive into a new function:
notmuch-show-advance. This new function does all the advancing
through a show buffer that notmuch-show-advance-and-archive did,
without all the invasive thread archiving. The return value of
notmuch-show-advance is nil if the bottom of the thread is not
reached, and t if it is.
notmuch-show-advance-and-archive is modified to just call
notmuch-show-advance, and then call notmuch-show-archive-thread if the
return value is true. In this way the previous functionality of
notmuch-show-advance-and-archive is preserved.
This provides a way for people to rebind the space bar to a more sane
function if they don't like the default behavior.