Local module forms in class declarations

[dsheets]

class my_class =
  let open My_module in
  let x = my_fun my_val in
object
  method x = x
end

is a syntax error.

class my_class =
  let module M = My_module in
  let x = M.my_fun M.my_val in
object
  method x = x
end

is also a syntax error.

[yallop]

There's some discussion of this under Mantis 6271.