s4:auth Change auth_generate_session_info to take flags

s4:auth Change auth_generate_session_info to take flags

This allows us to control what groups should be added in what use
cases, and in particular to more carefully control the introduction of
the 'authenticated' group.

In particular, in the 'service_named_pipe' protocol, we do not have
control over the addition of the authenticated users group, so we key
of 'is this user the anonymous SID'.

This also takes more care to allocate the right length ptoken->sids

Andrew Bartlett