Cantera's mechanism conversion scripts are now installed in the main
Cantera directory, so processing should work fine as long as Python is
on the path, whether or not the Cantera Python module is installed.
CanteraError inerits from std:exception, so now it has a what() method
that is used to print a message describing the exception. Adding an
exception to the Cantera error stack now requires explicitly calling
the .save() method.