Check tests for reporting testing changes automaticaly

As discussed in dev list https://lists.launchpad.net/yade-dev/msg06667.html, it would be usefull to test a set of typical simulations after commits and store the results somewhere, to help find out which revision invalidated something.
A modified script output would not be considered a failure by default, as opposed to regression tests, and the interpretation of the output (regression/improvment) would be left to the users adding tests, else it could make commiting excessively difficult.

Available in r2661.