Fixed bug 438: Bookmark menu items need to limit icon size

	* libnautilus-extensions/nautilus-icon-factory.h:
	Defined a new standard icon size, NAUTILUS_ICON_SIZE_FOR_MENUS.
	None of the existing standard sizes look good in menus.

	* libnautilus-extensions/nautilus-file.h,
	* libnautilus-extensions/nautilus-file.c
	(nautilus_file_is_mime_type): New function, compares against
	a particular MIME type so the caller doesn't have to get the
	MIME type and worry about whether to free it or not.

	* libnautilus-extensions/nautilus-icon-factory.c:
	(get_larger_icon_size),
	(get_smaller_icon_size): Include NAUTILUS_ICON_SIZE_FOR_MENUS
	when looking for the next size.
	(str_has_svg_suffix): Removed this function.
	(nautilus_icon_factory_get_icon_for_file): Use
	nautilus_file_is_mime_type to check for SVG instead
	of checking file suffix.
	(path_represents_svg_image): New function.
	(load_specific_image): Use path_represents_svg_image to
	check for SVG instead of checking file suffix.

	* libnautilus-extensions/nautilus-bookmark.c:
	(create_pixmap_widget_for_bookmark): Use
	NAUTILUS_ICON_SIZE_FOR_MENUS.
	* src/nautilus-window-menus.c (append_bookmark_to_menu):
	Use NAUTILUS_ICON_SIZE_FOR_MENUS.