Sort test cases by file name and line number before running them natively

[pgoodman]

It's helpful to run the test cases in a "logical" order. The order in which they are registered with DeepState is technically undefined, though one can expect it to be in reverse order of the appearance of the tests in the file, with the ordering across files as unspecified.

The Python symbolic executors sort tests before running them, which means that if only one process worker (the default) is used to run the test suite then that process then the ordering will look sane.