* app/xcf/xcf-save.c: when saving a text layer, store an extra
	parasite that holds all information about the text.

	* app/xcf/xcf-load.c: if a "gimp-text-layer" parasite is found and
	it can be successfully deserialized to a GimpText object, convert
	the layer to a text layer and remove the parasite.

	* devel-docs/parasites.txt: documented the new "gimp-text-layer"
	parasite.