COM: by value structs do not work

[the-snork]

Expected behavior and actual behavior

Think of a method (e.g. in PyCOMTest.idl)

HRESULT InStruct( [in] TestStruct1 inStruct );

Here, the structure is given by value.

The calls to InStruct end up with DISP_E_BADVARTYPE instead of S_OK.

Steps to reproduce the problem

Consider #2560 as merged.

After changing the server as in the scenario, just add

    data = module.TestStruct1()
    coclass.InStruct(data)

to TestMakePy in testPyComTest.py