Proposed change to libraries

[Richard A. O'Keefe]

	The bad news is that F must be allowed to be a "tuple fun" too,
	to keep backward compatibility.
	
	Thus the revised code must look like this:
	
	map(F, [H|T]) ->
	  [F(H)|map(F, T)];
	map(F, []) when is_function(F) ->	%% andalso is_fun_arity(F) == 1
	   [];
	map({M,F}, []) when is_atom(M), is_atom(F) ->
	   [].
	
	That should still give the Dialyzer more information about the type.
	
Everywhere we have an argument that should be a function but might not
always be applied we are going to have the same problem.  A fix that adds
an extra clause is going to be a pain.

We need
	is_applicable(F, N)
	- succeeds or returns true when N is a non-negative integer
          and F is such that F(T1,...,TN) would make sense
	- fails or returns false otherwise
	is_applicable(F)
	- succeeds or returns true when there exists an N such that
	  is_applicable(F, N) would succeed or return true
	- fails or returns false otherwise

Then
    map(F, [F|T]) -> [F(H)|map(F,T)];
    map(F, []) when is_applicable(F, 2) -> [].