Transient Mark Mode on by default

[Chong Yidong]

Thanks for all those who contributed to the recent discussion on the
list.  I've discussed this some more with Stefan, and the result is
that Transient Mark Mode is now turned on by default, in the trunk.

I have updated etc/NEWS accordingly.  The documentation now needs to
be updated accordingly.  I am already partway through updating the
Emacs manual, and will check in these changes over the next few days.
When I'm done, I'll inform the list and welcome additional
corrections.

Would anyone like to check the tutorial and the Lisp manual?