r9505: Work on GENSEC and the code that calls it, for tighter interface

r9505: Work on GENSEC and the code that calls it, for tighter interface
requirements, and for better error reporting.

In particular, the composite session setup (extended security/SPNEGO)
code now returns errors, rather than NT_STATUS_NO_MEMORY.  This is
seen particularly when GENSEC fails to start.

The tighter interface rules apply to NTLMSSP, which must be called
exactly the right number of times.  This is to match some of our other
less-tested modules, where adding flexablity is harder.  (and this is
security code, so let's just get it right).  As such, the DCE/RPC and
LDAP clients have been updated.

Andrew Bartlett