set Type on memory strip

we need to set Type on memory strips so we can convert to the output
format correctly, thanks philipgiuliani

see https://github.com/jcupitt/libvips/issues/120

TODO

@@ -1,9 +1,3 @@
-- try:
-
-	vips colourspace 16bit.tif 8bit.tif sRGB
-
-  to convert a RGB16 image to a sRGB one ... you get RGB in 8bit.tif, but it's
-  still 16-bit
 
 - can we use postbuild elsewhere? look at use of "preclose" / "written", etc. 
 

libvips/foreign/dzsave.c

@@ -39,6 +39,9 @@
  * 18/4/14
  * 	- use libgsf for output so we can write to .zip etc. as well as the
  * 	  filesystem
+ * 8/5/14
+ * 	- set Type on strips so we can convert for save correctly, thanks
+ * 	  philipgiuliani
  */
 
 /*
@@ -859,6 +862,10 @@ strip_init( Strip *strip, Layer *layer )
 		strip_free( strip );
 		return;
 	}
+
+	/* Type needs to be set so we know how to convert for save correctly.
+	 */
+	strip->image->Type = layer->image->Type;
 }
 
 static int