OPENWRITE filename

	command.  Opens the named file for writing.  If the file already
	existed, the old version is deleted and a new, empty file created.

	OPENWRITE, but not the other OPEN variants, will accept as input
	a two-element list, in which the first element must be a variable
	name, and the second must be a positive integer.  A character
	buffer of the specified size will be created.  When a SETWRITE is
	done with this same list (in the sense of .EQ, not a copy, so
	you must do something like
		? make "buf [foo 100]
		? openwrite :buf
		? setwrite :buf
		    [...]
		? close :buf
	and not just
		? openwrite [foo 100]
		? setwrite [foo 100]
	and so on), the printed characters are stored in the buffer;
	when a CLOSE is done with the same list as input, the characters
	from the buffer (treated as one long word, even if spaces and
	newlines are included) become the value of the specified variable.

