[F&O] IBM-FO-018: Request for copy function

(IBM-FO-018) Section 15, Functions and Operators on Sequences: There 
should be a "copy" function that returns an exact copy of its input 
sequence, with new node identities but preserving type annotations. 
Otherwise there is no way to make a copy of a node without wrapping it in 
a constructor, which the user may not wish to do.

--Don Chamberlin