Extends are not handled correctly in InstExtends

[Per Östlund]

The following model:

package P
  model A
    model B
      extends C;
    end B;

    B b;
  end A;

  model C end C;
end P;

model D
  extends P.A;
end D;

gives the error message:

[extends2.mo:4:7-4:16:writable] Error: Base class C not found in scope D.B

This is probably because when D extends P.A, InstExtends copies the contents of P.A into D. But P.A.B extends C, which is not reachable from D.

[Per Östlund]

Added a component to the A model, because otherwise it doesn't seem like the error is triggered anymore.

[Per Östlund]

The test case mofiles/InnerOuterWithExtends is no longer working because of this bug when SCodeFlatten is used by default, so I have moved it to failing tests. Please move it back to working tests when this bug is fixed.