Fix bug in getTotalCentrifugalForces() found by Justin Si and reported in issue 112.

Fixes issue #112.

This method incorrectly used the articulated body inertia when it should have been using the body spatial inertia.This was a localized problem in that reporting method; it didn't actually reflect the inertial forces that Simbody uses internally; those were correct.

Also added some missing test cases which should have been there in the first place!