Integrate new distrib stochastic test cases

[mhucka]

Lucian has created a bunch of test cases for the SBML distrib package. These should be incorporated into the main test suite.

Steps include at least the following:

• incorporate the files from Lucian's repo
• rewrite the README file in the stochastic subdirectory because the contents will no longer be solely from the DSMTS
• add instructions for using the new cases
• create a new test cases release

[luciansmith]

Well, step 1 is 'ensure that the expected results are accurate'. And, I suppose, there's also the possibility that some of the csymbols being tested in that suite will not end up in the final version of the package, if nobody implements support for them.

[luciansmith]

These are now released!