nowarn_unused_function should be transitive

[Anthony Shipman]

It would be nice if this declaration

	-compile([{nowarn_unused_function, {f, 0}}]).

meant that any functions that are only reachable from f are also treated as 
nowarn.
-- 
Anthony Shipman                    Mamas don't let your babies 
als@REDACTED                   grow up to be outsourced.