Check for mpt_demo1 as an M-file in Cinf.

Prior, if a variable named mpt_demo1 was defined the function would run,
even if the mpt toolbox was not provided.
Reoriented logic in parseOptions of Cinf

Flattened out the logic structure, made it easier to read. Also used the
dynamic field assignment instead of setfield.
Check for mpt_demo1 as an M-File in Pre

Before, it would just check if mpt_demo1 existed, even if it was a
variable. This could lead to a variable mpt_demo1 and no mpt toolbox,
which is required for Pre to run.