Parameters with optional arguments must have their arguments in the same parameter (joined) if given.

This is to avoid confusion, when for example a parameter is inserted into the
command line accepting an optional argument. If the next parameter was another
option, then the parameter was considered to have no argument, but if the next
parameter was something non-option (like a file name), then it was considered
to be the optional argument.

From now on, only required arguments may reside in the next parameter.