s4:server: avoid calling into nss_winbind from within 'samba'

s4:server: avoid calling into nss_winbind from within 'samba'

The most important part is that the 'winbind_server' doesn't
recurse into itself. This could happen if the krb5 libraries
call getlogin().

As we may run in single process mode, we need to set
_NO_WINBINDD=1 everywhere, the only exception is the forked
'smbd'.

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Autobuild-User(master): Stefan Metzmacher <metze@samba.org>
Autobuild-Date(master): Wed Jul 10 23:18:06 CEST 2013 on sn-devel-104