* libnautilus-extensions/nautilus-icon-container.c,
* libnautilus-extensions/nautilus-icon-container.h:
(nautilus_icon_container_set_label_font_for_zoom_level):
New function to set the font for a zoom level.

(nautilus_icon_container_initialize),
Initialize to fonts to a well known font.  Dont look at font
preferences here.  Fonts should be suppied by the icon container
user.

* src/file-manager/fm-icon-view.c:
(fm_icon_view_update_icon_container_fonts),
New function to update the icon container's zoom level specific
fonts.

(directory_view_font_familiy_changed_callback),
(fm_icon_view_initialize),
(fm_icon_view_destroy),
Keep track of font familiy preference changes and update the icon
container fonts as needed.

(create_icon_container):
Update the fonts for the first time when the icon container is
created.