SETWRITE filename

	command.  Makes the named file the write stream, used for PRINT,
	etc.  The file must already be open with OPENWRITE, OPENAPPEND, or
	OPENUPDATE.  If the input is the empty list, then the write stream
	becomes the terminal, as usual.  Changing the write stream does not
	close the file that was previously the write stream, so it is
	possible to alternate between files.

