This portion of the Matlab test suite was being skipped on some platforms and/or
Matlab versions. Switching to the 'classdef' style of tests fixes the problem.
When instantiating a phase from a .cti file, do the conversion in memory,
without writing the XML representation to disk. This eliminates the unrequrested
XML files that Cantera normally generates, and also avoids errors when running
Cantera from a directory where the user does not have write permissons.
