[Cfp-interest 1460] revised proposed note about C math functions not required to be correctly rounded

[David Hough CFP]

After discussion with Jim, a better place for the note is in F.10,
revised as follows -

 IEC 60559 specifies correct rounding for the operations in the table in F.3, 
 "Binding of operations recommended by IEC 60559",
 and thereby preserves useful mathematical properties such as symmetry,
 monotonicity, and periodicity.   
 The corresponding functions with reserved cr_ prefixed names (7.31.8) 
 do the same.
 The C functions in the table in F.3, 
 "Binding of operations recommended by IEC 60559", however, 
 are not required to be correctly rounded, 
 but implementations should still preserve as many of these
 useful mathematical properties as possible.