Add RPC_S_SEC_PKG_ERROR to the list of "hard" errors.

Allows to start console applications in a new window (as Windows does).

rpcrt4: Never allocate memory for the discriminant in union_arm_unmarshall as the memory is part of the union and has already been allocated.

rpcrt4: Check to make sure there is enough data in the buffer during unmarshalling, so that the code doesn't try to read beyound the end of the buffer.

rpcrt4: Even though FC_ENUM16 is an unsigned type, the highest allowable value that can be marshalled is SHRT_MAX, not USHRT_MAX.

CoFreeUnusedLibraries doesn't do anything and COM_FlushMessageQueue 
won't actually allow any RPCs to be processed as the apartment has 
already been destroyed.