invoke broken for constructors

[simonster]

More fallout from #8712:

julia> type A; end

julia> invoke(A, ())
ERROR: type: invoke: expected Function, got Type{A}

julia> method_exists(A, ())
ERROR: type: method_exists: expected Function, got Type{A}

julia> applicable(A)
ERROR: type: applicable: expected Function, got Type{A}

Maybe method_exists and applicable are not so useful since they would always be true for constructors due to the call fallback, but invoke still seems useful. This can currently be worked around as invoke(call, (Type{A},), A), but it would be nice if this weren't necessary.

[garborg]

Any thoughts about invoke's future? (I've been lazy about adding workarounds to get DataFrames' tests passing -- it's probably time. Just curious.)

[JeffBezanson]

Fixed by #13412.