BSTR caching

[Dan Kegel]

Hi Markus,
Wine development is driven by test cases checked in to the
Wine source tree.  Please extend the test cases in
dlls/oleaut32/tests to verify that oleaut32 is caching BSTRs
properly, and make sure that test passes on Windows
and is marked todo_wine.
Once we have a test case like that checked into the Wine
source tree, we'll be in better shape to accept a patch
that fixes bug 12460.
Thanks!