Added SIMFSI::preprocess invoking the simular methods of the substep solvers. Merged the three methods returning the solid forcing-function into one. Added convenience methods SIMGridMover::[sg]etBDForder. Allow the BDF object to have order=0 (meaning don't use BDF). git-svn-id: http://svn.sintef.no/trondheim/IFEM/trunk@2363 e10b68d5-8a6e-419e-a041-bce267b0401d