switched to a new way of handling unions, so that we can handle

switched to a new way of handling unions, so that we can handle
alignment correctly for unions that have non-uint16 discriminants

fixed the union handling in srvsvc.idl. (metze, please take a look at
the changes, your IDL did match what was one the wire in most cases,
but isn't the way IDL is usually coded)
(This used to be commit 7b5d0287298e8505e0ec7b22d75d9f9a8a610031)