Macro:	PROVIDE - easy macro to clone objects in rooms if missing there

Synopsis:
	void PROVIDE(string name, string path)

Description:
	Checks if an item that responds to 'name' is already present
	(in the room), and produces a clone from 'path' if it is not.

Note:
	This is actually a macro for "if (!present(name)) PRODUCE(path)".

See also: lib/PRODUCE, lib/MACROs