ole32: Handle NULL sub-objects correctly in the STGMEDIUM user marshaling functions so that no further data in marshaled or unmarshaled.

Previously it was hardcoded to 16, so only the NTLM provider would work correctly.

rpcrt4: Call CompleteAuthToken if InitializeSecurityContext returned a code that says it should be called.

Currently, the only security provider that requires this is the Digest 
one, which we don't really care about, but is supported for completeness.

This reduces the amount of code and ensures that the parameters passed 
to it stay the same, apart from the previous context and the output 
buffer description.

rpcrt4: Retrieve the maximum token length from the security provider rather than using a hardcoded and rather small limit.

Copy the OXID_INFO from the stub manager, if available, in 
proxy_manager_construct. Otherwise, attempt to resolve it.

Use ipidRemUnknown from OXID_INFO in the proxy manager instead of 
magically generating the IPID for RemUnknown.

rpcrt4: Implement associations which are intermediary objects that track the relationship between the client and a given endpoint on the server.

Use these to encapsulate the connection pool so that the lifetimes of 
connections are properly handled again.

The tests shows that CBGetTextAreaHeight was using a bad formula.