Fix debug build to address issue #10

Travis fails to build on gcc due to wrapping.  Creating PR in the meantime since issue is unrelated to this fix.
Ajay, if you want to check the inertia without throwing an exception there is a method [SimTK::Inertia::isValidInertiaMatrix()](https://simtk.org/api_docs/simbody/api_docs33/Simbody/html/classSimTK_1_1Inertia__.html#a09065c454fb39eec2dee757f63ff277e).

That is a static method that takes a `SimTK::SymMat33` and tells you whether it could be a legitimate inertia matrix. A drawback is that it is just a true/false return; you don't get any more details as you get with the exception message. The code is [here](https://github.com/simbody/simbody/blob/master/SimTKcommon/Mechanics/include/SimTKcommon/internal/MassProperties.h#L432) for the validity checker and [here](https://github.com/simbody/simbody/blob/master/SimTKcommon/Mechanics/include/SimTKcommon/internal/MassProperties.h#L526) for the current Debug-only exception thrower.