popup: follow GDK_SCALE on HiDPI

The popup was 32-pixel rows whatever the display; next to 2x application
text it was small. Its metrics now scale with the daemon's GDK_SCALE,
the setting the applications use.

popup_layout.c

@@ -5,6 +5,8 @@ enum {
 	Asciitofull = 0xFEE0,
 };
 
+int popupscale = 1;
+
 static void
 fill(u32int *buf, int n, u32int color)
 {