Partial fix for bug #12679 (https://gna.org/bugs/index.php?12679).
This bug was reported by Michael Funk (mifu att nmr dot mpibpc dot mpg dot de).
The problem was that the data for the graph was numpy arrays, and only lists were being checked for.
Authored by: bugman 2008-12-04
Parent: [r8134]
Child: [r8136]
