Duplicate UUID in oleaut32:tmarshal test

[Thomas Faber]

I just tried running midl on dlls/oleaut32/tests/tmarshal.idl and it
complained:
tmarshal.idl(83) : error MIDL2270 : duplicate UUID. Same as : ItestDual [ Interface 'ITestSecondDisp'  ]

This doesn't seem like it's intentional. But just giving
ITestSecondDisp a new uuid causes the following test failures on
Windows:
tmarshal.c:1861: Test failed: external_connections = 2
tmarshal.c:1864: Test failed: external_connections = 2
tmarshal.c:192: Test failed: fLastReleaseCloses = 1

I could try to figure this out, but it's probably better if someone
familiar with the subject could have a look instead.

(also, assuming this is a bug in the test, we might want to add that
check to widl, it seems pretty useful ;])

Thanks,
Thomas