Fix remaining bugs with the CPC ROM version.

- Fix an extra const for the icons that shouldn't be there for the ROM
  version. It is there in the loadable version of the DSC files to
  workaround linker script limitations, but in the ROM it results in
  trying to write to ROM when the icons are added to the desktop
- Fix a bug (broken code generation by the compiler?) that leads to
  vertical lines in windows not stopping where they should and going all
  the way down the screen (clipping was applied when it shouldn't,
  leading to an overflow)
diff --git a/contiki-cpc/apps/directory-dsc.c b/contiki-cpc/apps/directory-dsc.c
index caa0b63..e36d606 100644
--- a/contiki-cpc/apps/directory-dsc.c
+++ b/contiki-cpc/apps/directory-dsc.c
@@ -36,7 +36,7 @@
 #include "dsc.h"
 
 /*-----------------------------------------------------------------------------------*/
-const DSC(directory_dsc,
+DSC(directory_dsc,
     "Directory reader",
     "dir.prg",
     directory_init,
@@ -66,6 +66,10 @@
 };
 #endif /* CTK_CONF_ICON_TEXTMAPS */
 
-static const struct ctk_icon directory_icon =
+static
+#if !BUILDING_FOR_ROM
+const
+#endif
+struct ctk_icon directory_icon =
   {CTK_ICON("Directory", directoryicon_bitmap, directoryicon_textmap)};
 /*-----------------------------------------------------------------------------------*/