This is of course a fairly naive initial implementation. We'd probably want to
batch up drawing operations, and only execute them on EndDraw() or Flush() to
reduce state setup overhead.

Aggregates are returned through an implicit parameter after the this/interface
pointer. Note that this follows the C++ convention, affected methods are not
callable from C with the Microsoft headers.

kernel32/tests: Add tests for partially received pipe messages after calling SetNamedPipeHandleState.

dds_get_outer AddRefs the inner surface when it creates the wrapper
surface. The wrapper releases only one reference when it is destroyed,
leaking one of the two. AddRefing in dds_get_outer makes sense because
this is also used by e.g. GetAttachedSurface, where it creates a new
wrapper for surfaces ddrawex didn't know about yet.