-Added currentVTKFileNumber method to the boxproblem and curWriterNum to

the vtkmultiwriter. This is needed for a correct output (of e.g. fluxes) of the coupled
models in case of a restart
-Corrected some typos



git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@7258 2fb0f335-1f38-0410-981e-8018bf24f1b0