[F&O] IBM-FO-019: Request for deep-distinct function

(IBM-FO-019) Section 15, Functions and Operators on Sequences: There 
should be a "deep-distinct" function that eliminates duplicate items from 
sequences. Duplicate atomic values should be defined by the "eq" operator. 
Duplicate nodes should be defined by fn:deep-equal(). In the case of 
duplicate nodes, the node that is retained should be 
implementation-dependent. This function is needed by queries that need to 
perform grouping where the grouping-key is a node (for example, grouping 
by <address> that has subelements <street> and <city>, or grouping by 
<author> that has subelements <first-name> and <last-name>.)

--Don Chamberlin