Ticket 467: Allow eqv? and eq? to return different answers on procedures as well as integers and characters

This proposal stems from remarks by Alaric Snell-Pym and Will Clinger on the r6rs public mailing list. If eq? is allowed to return #f on two procedures when eqv? nevertheless returns #t, as is already the case for numbers and characters, then more intelligent implementation-specific procedure comparisons using eqv? are possible, while still keeping eq? simple enough to inline easily.

Note that this is orthogonal to the question of #460, how eqv? works on procedures. There should be little or no backward-compatibility hit for this change