[ctml_writer] Improve error reporting
[ctml_writer] Improve error reporting

Print a more useful traceback for cases where exceptions are raised in ctml_writer.

git-svn-id: e76dbe14710aecee1ad27675521492cea2578c83@2799 02a645c2-efd0-11dd-984d-ab748d24aa7e

Cantera/cantera-svn,Cantera/cantera-svn,Cantera/cantera-svn,Cantera/cantera-svn,Cantera/cantera-svn,Cantera/cantera-svn