Tester updates for testing tutorials

The MR adds an option to the Tester code to allow the executable specified in the .tst file to be overridden on the command-line. This is to allow the use of executables which lie elsewhere in the build tree, not just in the directory containing the Tests directory.

It also fixes support for input files to be located in a different directory to the test file itself. It would previously fail if the list of dependent files included a relative path to a file in a different directory.

Finally, there are also a couple of tweaks to the submodule so git ignores it when things have changed.