Extract better font information from the GTK >= 3.2 font chooser.

Extract better font information from the GTK >= 3.2 font chooser.

* gtkutil.c (xg_get_font): Rename from xg_get_font_name.  When
using the new font chooser, use gtk_font_chooser_get_font_desc to
extract the font descriptor instead of just the font name.  In
that case, return a font spec instead of a string.
(x_last_font_name): Move to this file from xfns.c.

* xfns.c (Fx_select_font): The return value can also be a font
spec.  Move x_last_font_name management to gtkutil.c.

* xfaces.c: Make font weight and style symbols non-static.

* lisp/frame.el (set-frame-font): Accept font objects.