RequireOrder: do not collect unrecognised options after a non-opt

RequireOrder: do not collect unrecognised options after a non-opt
The documentation for RequireOrder says "no option processing after
first non-option", so it doesn't seem right that we should process the
rest of the arguments to collect the unrecognised ones.  Presumably
the client wants to know about the unrecognised options up to the
first non-option, and will be using a different option parser for the
rest of the command line.

eg. before:

Prelude System.Console.GetOpt> getOpt' RequireOrder [] ["bar","--foo"]
([],["bar","--foo"],["--foo"],[])

after:

Prelude System.Console.GetOpt> getOpt' RequireOrder [] ["bar","--foo"]
([],["bar","--foo"],[],[])