Fix bug in OutputCheck program that calls driver. If OutputCheck is
installed by pip then when we run the test suite the installed version
gets used rather than the git repo version because the system import
is attempted and only if that failed would we look in the git repo
for the OuputCheck package.

Now we do it the other way round so if OutputCheck if being run from
the Git repository we use that in preference to a system installed
version.
Added --dump-input-file command line option to show input (useful for
pipes) to OutputCheck. A test case for this option has been added.