I have reworked the show-mode message/thread archiving improvements from
two now-obsolete patch sets:

id:"1325975294-646-1-git-send-email-jrollins@finestructure.net"
id:"1325986015-22510-1-git-send-email-jrollins@finestructure.net"

All the "delete" stuff has been removed from this series, and I just
focus on improving the functions associated with message and thread
tagging, archiving, and navigation.  I also incorporated some good
suggestions from Aaron Ecay to make things "lispier".

The first five patches should be non-controversial and just improve the
available functions without changing any visible behavior.  Together
they make it much easier for users to create useful custom key bindings
to achieve custom tagging and navigation operations.

The last patch changes the default keybind for the 'a' key to archive
just the current message, and not the entire thread.  In my opinion this
is a *much* more sensible binding for this key.  I actually rebound to
this immediately after I started using notmuch long ago.  It also adds a
new 'A' that performs the old function to archive the entire thread and
move on.

jamie.