McStas 2.6 rc: Reinstate %Example for many instruments, e.g. IN6

[willend]

Dating back to the time where we were insecure about results from instruments with Isotropic_Sqw, many instruments had %Example -> Example to prevent the tests from running.

As we are now preparing release of 2.6 and later a 3.0beta, we should reestablish as many tests as possible, e.g. complex instruments that feature GROUP's.