[PATCH 0/5] MR1068: combase: CoMsgWaitForMultipleHandles

[Kevin Puetz (＠puetzk)]

Some preliminary cleanups (split off from !969)

- extend an existing `wine_todo` test to show that DDE messages cause spurious calls to IMessageFilter::MessagePending (the same as RPC ones)
  I have no current ideas for fixing this, just demonstrating the behavior (before refactoring the code in ways that won't change this)
- extract a helper `com_filter_messagepending` for the interactions between `CoWaitForMultipleHandles` and IMessageFilter::MessagePending 
- Pull the remaining use of `PeekMessageW` into the existing `com_peek_message` helper
- one behavior fix, to make `RPC_E_CALL_CANCELED` actually work