r4777: added a smb_composite_sesssetup() async composite function. This

r4777: added a smb_composite_sesssetup() async composite function. This
encapsulates all the different session setup methods, including the
multi-pass spnego code.

I have hooked this into all the places that previously used the
RAW_SESSSETUP_GENERIC method, and have removed the old
RAW_SESSSETUP_GENERIC code from clisession.c and clitree.c. A nice
side effect is that these two modules are now very simple again, back
to being "raw" session setup handling, which was what was originally
intended.

I have also used this to replace the session setup code in the
smb_composite_connect() code, and used that to build a very simple
replacement for smbcli_tree_full_connection().

As a result, smbclient, smbtorture and all our other SMB connection
code now goes via these composite async functions. That should give
them a good workout!
(This used to be commit 080d0518bc7d6fd4bc3ef783e7d4d2e3275d0799)