Call Arity: In "e x", the result of "x" is not shared

in contrast to "e (f x)", where CorePrep will turn it into "let y = f x

in e x". So in

let f = ... in e (f x)

we know that f is called at most once, but in

let f = ... in e f

we do not know that.

Previously Call Arity would assume that in "e x", "x" is evaluated at

most once. This rarely would make a difference (the argument "x" is

analized with an incoming arity of 0, so no eta-expansion would be done

anyways), but of course this should still be fixed.

This fixes Trac #11064.

Note the corresponding code dmdTransformThunkDmd in DmdAnal.