Handling of iso directory depth restrictions on tree creation time.

Note that this doesn't involve the RR reparent. It just ignore the files 
that break iso restrictions (see ECMA-119, 6.8.2.1).

src/messages.h

@@ -15,6 +15,9 @@
 
 #include "libiso_msgs.h"
 
+/** File cannot be added to image (ignored) */
+#define LIBISO_FILE_IGNORED         0x00030100
+
 /** Can't read file (ignored) */
 #define LIBISO_CANT_READ_FILE		0x00031001
 /** Can't read file (operation canceled) */