The underlying type-check was correct, but I forgot to consider it in
the outer code, and embarassingly never tested this case.
rdar://problem/28435922
We strip the first input type on instance methods like,
struct S { func foo(T) -> U } // (S)->(T)->U
but we should not do that when it's actually a curried instance method,
such as S.foo.
If we're completing in a context that expects a function type, try to
match methods/functions as function references before trying them as
calls. This means that
func take(_: (Int)->()) {}
func foo(a: Int) {}
take(#^A^#) // completes foo(a:) instead of foo(a: {#value#})
Note: doesn't yet work with generic types.
rdar://problem/28435922
