Bugs in GenericOil, real-equality-with-0

GenericOil references a type, Density, and a variable, T, neither of which is defined. Density is presumably SI.Density, T should be Toperating as this is done in dynamicViscosity()? (Though I'm not sure if a function should access a parameter in the enclosing scope).

ConstVolumeSource contains an if-equation that compares a Real parameter q with 0, however since the right-hand-side of the resulting equation is multiplied by q the same effect can be achieved by forcing q to be evaluated.

Other change (removal of Streams.print() in favor of assert()) in previous pull-request has been reverted