[F&O] IBM-FO-028: Inconsistent function signatures

(IBM-FO-028): Section 9.5, "Arithmetic Functions on Durations": In the 
table at the beginning of this section, op:multiply-yearMonthDuration() 
and three other functions are said to take operands of type xs:decimal. 
But in the actual signatures of these functions, the operands are 
specified as xs:double rather than xs:decimal.

--Don Chamberlin