* src/macfont.m (macfont_family_cache): New variable.
(syms_of_macfont): Initialize it.
(macfont_available_families_cache): New variable.
(macfont_invalidate_family_cache, macfont_get_family_cache_if_present)
(macfont_set_family_cache, macfont_invalidate_available_families_cache)
(macfont_handle_font_change_notification)
(macfont_init_font_change_handler)
(macfont_copy_available_families_cache): New functions.
(macfont_create_family_with_symbol): Use font family caches.
(macfont_list, macfont_list_family): Use
macfont_copy_available_families_cache instead of
mac_font_create_available_families.