Hi all,

I've taken a little bit of time to rethink how I wanted this to
work. Namely:

1. Trying to make a single hook do two separate things (determining
whether to prevent tab closing and tasks on tab close) just made things
overly complicated. Tab close prevention has been split off into a new
hook, `tab-bar-prevent-close-functions'.

2. I realized that it's possible when creating a new tab to just delay
the actual creation of the tab in the frame's tab list. This makes it
possible to directly modify the tab passed in to
tab-bar-tab-post-open-functions, ie `(setf (alist-get 'name tab) "New Name")`
from within a hook function. This means it's not really
necessary to make new accessors.

To be honest, I've been having a hard time coming up with good examples
of how to use these hooks that aren't arbitrary, contrived, or don't
otherwise require support in other places (more than one of the possible
examples I was thinking of works best when another mode or command, such
as gdb or mpc, has the ability to automatically start in a new
tab).

New patch, as well as a file of examples for the new hooks,
follow. Again, these new hooks still need to be documented in the
manual, which I will be glad to do as soon as a design is nailed down.

Thanks,
-- 
~Robert Cochran