Document: Use a better base64 decoder to read static image data.

Document: Use a better base64 decoder to read static image data.

        * src/test/java/org/glom/web/server/libglom/DocumentTest.java:
        getNodeTextChildAsValue(): Use the apache commons base64 decoder
	instead of the gwt one, because it correctly decodes the strings
	from g_base64_encode(). It is probably more correct.
	The newlines might be confusing the gwt decoder.