clipboard/selection: customization vs. rebinding

[David De La Harpe Golden]

As a feature freeze is rapidly coming up, I'd like (...for some value of 
like...) to raise this one more time:

I remain concerned it's too hard to revert to "classic" emacs behaviour 
absent any UI for rebinding beyond "use emacs lisp". Right now, there's 
a mix of customization variable adjustments and a rebinding involved.

It's unlikely that a general customization-type UI for bindings will 
appear in the immediate future, so I propose for 24 binding mouse-2 back 
to mouse-yank-at-click but with the addition of boolean customization to 
control the precise behaviour to allow the desired fd.o-type behaviour. 
 Then one need only adjust customization variables to select between 
the classic and fd.o-type behaviours, rather than both customization 
variables and global bindings, which has been a source of confusion and 
misunderstanding (especially on platforms without a primary).

OTOH, if the mouse-2 binding is not reverted to mouse-yank-at-click, 
then note there are other binding sites that will need adjustment to 
mouse-yank-primary to match the new binding of mouse-2 for consistency 
(e.g. the fringes, where mouse-2 still does a mouse-yank-at-click).