functions with ntdll equivalent
- replaced status setter/getter for wine async structures with direct
access to a (now included) IO_STATUS_BLOCK structure
- since we now have a IO_STATUS_BLOCK in async_private, we no longer
need in most of the user (derivated) structures a field for
LPOVERLAPPED (it's stored as the IO_STATUS_BLOCK)
- rewrote the async.h users accordingly
- implemented ntdll.Nt{Read|Write}File and let
kernel32.{Read|Write}File(Ex)? use those new ntdll functions
- rewrote smb read/write interfaces to be more ntdll stylish (no
overlapped yet)
- calling the "call_completion" method unconditionally in finish_async
(introduced by me) was wrong, because the thread may never be in an
alertable wait state -> call it only if user completion function is present.
- We need two constant "ops" objects, one with and one without call_completion
method (the event field may NOT be used to determine whether the completion
must be called or not).
