C forder could take verbose argument

[jangorecki]

That would be handly when we have a C function fun1 that uses datatable.verbose option, and this function calls forder internally. We are mostly interested in verbose output of fun1 rather than forder. Yet good control could be provided by calling something like forder(verbose = verbose-1L). That allows to print verbose messages from everything when bigger value is provided to verbose.
This feature is already implemented in #4491