bug#29627: 25.3; x-show-tip does not display text when x-gtk-use-tooltips is nil and left/right-margin-width is set

[martin rudalics]

> Thanks, fixed on the emacs-26 branch.

Could you please tell why such a harsh treatment was necessary?  In
particular why (1) showing the margins initially failed and (2) instead
of just forcing the window margins have zero width you made the window a
pseudo-window.

Thanks, martin