[Elementary] Make it possible to lookup icons from Freedesktop in Elm_Icon.

[Elementary] Make it possible to lookup icons from Freedesktop in Elm_Icon.

With these changes, Elm_Icon will also look up icons from the chosen
Freedesktop (fd.o) icon theme.  Since this might incur in some performance
penalties if you're sure only theme icons will be used, icon lookup order
may be specified with the elm_icon_order_lookup_set() function call; using
the lookup parameter as follows:

 - ELM_ICON_ORDER_FDO_THEME (default) will look up first fd.o, then the theme;
 - ELM_ICON_ORDER_THEME_FDO will look up first the theme, then fd.o;
 - ELM_ICON_ORDER_FDO will look up only fd.o; and
 - ELM_ICON_ORDER_THEME (old behaviour) will lookup only from the theme.

Elm_Icon will also try to use a different resolution image if the widget is
resized and the image source is fd.o.

fd.o support requires Efreet, but it should work nicely (falling back to the
old behaviour) if it isn't available.

SVN revision: 53433