Misleading error for records

[mtzguido]

module A

let foo () : int & bool = { x=1 }

* Error 118 at A.fst(3,28-3,29):
  - Field 'x' is redundant for type FStar.Pervasives.Native.tuple2
  - Missing fields: '_2', '_1'

1 error was reported (see above)

This error should say instead that tuple2 is not a record, or that we expected tuple2 and got a record.