r4769: added a smb_composite_connect() function that provides a simple async

r4769: added a smb_composite_connect() function that provides a simple async
interface to a complete SMB connection setup. Internally it does:

  - socket connection
  - session request (if needed)
  - negprot
  - session setup
  - tcon

This is the first example of a composite function that builds on other
composite components (the socket connection is a composite function,
which is used as a building block for this function). I think this
will be quite common in composite functions in the future, building up
ever more complex composite functions from smaller building blocks,
while hiding the details from the caller.

There are two things missing from this now. The first is async name
resolution routines (wins, bcast, DNS etc), and the second is that
this code currently only does a NT1 style session setup. I'll work on
adding spnego and old style session setup support next.
(This used to be commit 6bc9e17f5c5236f662c7c8f308d03e6d97379b23)