winhelp: winhelp >3.0 files always use 0x4000 as a divisor in TOPICPOS regardless of DecompressSize.

rpcrt4: Set the destination pointer in PointerUnmarshall before calling the referenced type's unmarshalling routine.

When a pointer that is dereferenced is encountered then this can result 
in a stale pointer (i.e. the one that is marshalled into the buffer for 
the embedded pointer unmarshalling case) being used instead of the one 
that was intended.

It varies on different versions of Windows, so we shouldn't test it for 
an exact value.

rpcrt4: Call IRpcChannelBuffer_GetDestCtx in NdrStubInitialize, just like we do in NdrProxyInitialize.

rpcrt4: Flesh out more of the IRpcChannelBuffer vtable to make the test_delegating_Invoke test succeed on Windows.