bug#56421: [PATCH] Make mouse-2 respect delete-selection mode

[Juri Linkov]

>> If you think we should be consistent, then I'd rather drop the patch
>> than add yet another defcustom.  It isn't hard to copy those lines to my
>> config anyway.
>
> Let's see if anyone else has an opinion here.

This should be the right thing to do, some time ago
we already discussed this because I had these uncommitted lines:

+(put 'mouse-yank-primary 'delete-selection 'yank)
+(put 'mouse-yank-at-click 'delete-selection 'yank)
+(put 'menu-bar-select-yank 'delete-selection 'yank)

BTW, I also had this line

+(put 'just-one-space 'delete-selection t)

but since M-SPC is bound to cycle-spacing now,
I'm not sure about M-SPC anymore.  How does
cycle-spacing handle regions?  Maybe it should
squeeze all consequent spaces to one space
everywhere in the region?