bug#57468: 29.0.50; Text cursor continues to blink when frame loses focus

[Po Lu]

I figured out how to reproduce the problem.  You have to keep the mouse
pointer inside the first frame while opening the second Emacs.  Then,
the focus sticks on the first frame because the X server totally messes
up reporting of XI_Leave events if the window manager does not set the
focus specifically on the client pointer (which the documentation is
adamant that you _can_ omit, so this is yet another X server bug.)

I installed a workaround on master.  It would be nice if all the people
who use Emacs without a window manager tried it out as well to see if it
leads to any unpleasant side effects, which it probably will, but I
don't know yet know what side effects there will be.

Thanks.