libdraw: refine hidpi font selection

Change-Id: Id1e6a2630713024a1925ad1341bb9c846f82e93e
Reviewed-on: https://plan9port-review.googlesource.com/1171
Reviewed-by: Russ Cox <rsc@swtch.com>

include/draw.h

@@ -308,6 +308,7 @@ struct Cachesubf
 struct Font
 {
 	char		*name;
+	char		*namespec;
 	Display		*display;
 	short		height;	/* max height of image, interline spacing */
 	short		ascent;	/* top of image to baseline */