Sticky tooltips

[Arthur Miller]

I played a bit, and it does not look so bad actually. I have played both
with 'propertized' widget and one with 'plain' text; the latter takes
less space on the screen; but it is just to switch comments and test the
propertized version in the patch. 

Adding a checkbox wasn't difficult part and modifiying x-show-tip
accordingly wasn't the hard part. x-show-tip in xfns.c is almost
unchanged minus the part for creating a new buffer and inserting the
string. However, I don't know where to look for mouse motion callback to
turn off automatic hiding on mouse move. Anyway, with patch it is
possible to see how it looks like, even if callback itself does not work.

I added a customize option tooltip-enable-sticky (off by default) which
takes effect only if gtk tooltips are disabled:

(setq x-gtk-use-system-tooltips nil
      tooltip-enable-sticky t)

It is just an idea how it might look and work to see if it is interesting
to have.

tooltip.el.patch
Description: tooltip.el.patch

xfns.c.patch
Description: xfns.c.patch