Update filename slicing for .dak rename.

ChangeLog

 2006-06-11  James Troup  <james@nocrew.org>
 
+	* dak/daklib/utils.py (validate_changes_file_arg): update filename
+	slicing to cope with new .dak filenames.
+
 	* dak/ls.py (main): add back 'heidi' as a valid argument for
 	-f/--format as people are using it in scripts and breaking that
 	without warning seems rude.

daklib/utils.py

@@ -608,7 +608,7 @@ argument:
 
     orig_filename = filename
     if filename.endswith(".dak"):
-        filename = filename[:-6]+".changes"
+        filename = filename[:-4]+".changes"
 
     if not filename.endswith(".changes"):
         error = "invalid file type; not a changes file"