Add get_disc_mode to image readers.

Add it in cd-info display.
Update regression tests.

I'm not sure disc_mode is all that helpful or correct.

lib/image_common.h

@@ -1,5 +1,5 @@
 /*
-    $Id: image_common.h,v 1.13 2004/07/17 22:16:47 rocky Exp $
+    $Id: image_common.h,v 1.14 2004/07/24 14:23:37 rocky Exp $
 
     Copyright (C) 2004 Rocky Bernstein <rocky@panix.com>
 
@@ -119,6 +119,16 @@ _get_cdtext_image (void *user_data, track_t i_track)
   
 }
 
+/*! 
+  Get disc type associated with cd_obj.
+*/
+static discmode_t
+_get_discmode_image (void *p_user_data)
+{
+  _img_private_t *p_env = p_user_data;
+  return p_env->disc_mode;
+}
+
 /*!
   Return the media catalog number (MCN) from the CD or NULL if there
   is none or we don't have the ability to get it.