tooltip frame uses (class mono) when processing defface specs

[Joe Wells <jbw@macs.hw.ac.uk>]

When processing defface specs, the tooltip frame uses alternatives
that select the characteristic (class mono).  Alternatives that select
(class color) or (class grayscale) are not used.

Can this please be changed, or at least made customizable?

I am trying to get the folding mode of AUCTeX to display nicer
tooltips.  It would be nice if it could effectively use the
fontification of hidden text in tooltips.  Right now, standard faces
don't show well in the tooltips, because their mono version is used.
It would be a big help if the standard face definitions showed nicely
on tooltip frames.

(Yes, there are other issues that also would need to be handled, like
the way the tooltip-show function replaces the face of the message
string with the face tooltip.  But that is in Emacs Lisp, and hence
easier to fix, perhaps by making tooltip-show not do that if the
message has a particular property on it.)

-- 
Joe