bug#28903: 26.0.90; Better `C-h k' help for mouse events

[Drew Adams <drew.adams@oracle.com>]

Click `mouse-1' in the left fringe. While `mouse-1' is depressed, before
you release it, you can see this in the echo area:

 left-fringe down-mouse-1-

When you release `mouse-1' you get the `C-h k' help:

 <mouse-1> (translated from <down-mouse-1> <mouse-1>) at that spot runs
 the command mouse-set-point...

The information about the click being in the fringe is lost - not
presented.  The binding of `mouse-1' is described.  Well, OK, that's the
key sequence that was bound to a command, so the help info is correct.

But it would be helpful if we said something more specific than just "at
that spot".  Especially because the binding of a mouse press or click
can be different at different "spots".  Can we not say something like
"in the left fringe" instead of "at that spot"?

Similarly, if you click in the minibuffer or echo area or...
Could we not mention where you clicked (or pressed or dragged)?

In GNU Emacs 26.0.90 (build 3, x86_64-w64-mingw32)
 of 2017-10-13 built on LAPHROAIG
Repository revision: 906224eba147bdfc0514090064e8e8f53160f1d4
Windowing system distributor 'Microsoft Corp.', version 6.1.7601