Disable double hires on exit.

A program being run afterwards might not even know about the existence of double hires. So it's our task to turn double hires off on exit.

targettest/apple2/dhgrshow.c

@@ -40,6 +40,7 @@ void main (void)
     }
     closedir (dir);
 
+    POKE (0xC05F, 0);
     tgi_uninstall ();
     videomode (old);
 }