BSD socket SO_REUSEADDR is not a complete match, but features like
"allow binding to a port immediately after closing it" seem to be compatible.

For now, those pointers are always null, anyway.

This patch initializes allocated pointers in PointerUnmarshall since later
code checks the value for NULL (specifically, NdrConformantArrayUnmarshall).

This initializes the memory for an [in] parameter.

include: Take care to not declare CtxtHandle and PCtxtHandle more than once when including both sspi.h and wincred.h.

inetcomm: Call InternetTransport_RegisterClass and UnregisterClass on process attach and detach respectively, to register a window class and initialize Winsock.

inetcomm: Use InternetTransport_ChangeStatus in InternetTransport_DropConnection so that the callback gets called.

Based on a patch by Rob Shearman.

inetcomm: Add a framework for connecting to a server and sending/receiving data asynchronously with callbacks being called in the context of the original thread, using window messages.