(fontset_compare_rfontdef): Fix plus/minus.

(fontset_compare_rfontdef): Fix plus/minus.
(reorder_font_vector): Change the arg preferred_family to font.
Prefer the spec matching with font.
(fontset_get_font_group): New function.
(fontset_find_font): Change the format of an element of a realized
fontset.  Use fontset_get_font_group.
(fontset_font): Try the current fontset, the default fontset, the
fallbacks of the current fonset, and the fallbacks of the default
fontset in this order.
(face_for_char): Delete the shortcut to use the current font.
(fontset_from_font): Don't set fonts for Latin in the fontset.