bug#3783: tutorial description of saving files is confusing

[Glenn Morris]

Some aspects of the description of saving files in the tutorial are
currently confusing.

In Emacs 21, the tutorial had a default-directory of ~, and a
buffer-file-name of ~/TUTORIAL (+ language extension).

This meant that when reading the TUTORIAL, it was possible to just do
C-x C-s to save a copy to one's home directory.

The tutorial still makes reference to this at a couple of places:

  >> Type C-x C-s, saving your copy of the tutorial.
     This should show "Wrote ...TUTORIAL" at the bottom of the screen.

and later on:

  Finally, type C-x C-f TUTORIAL <Return>
     to come back to the tutorial.

This doesn't work as described, because the tutorial has no associated
file name now. So, for example, typing C-x C-s prompts for a file name
rather than simply saving it.

I don't know the right way to fix this. The concept of a buffer not
being associated with a file is not introduced until later on in the
tutorial, nor is the use of C-x b to switch buffers. Nor do I know how
to hook the normal C-x C-s saving into the special saving that the
tutorial uses now.