r11809: Make dcerpc_bind_auth async.

r11809: Make dcerpc_bind_auth async.

This also removes dcerpc_bind_auth_password, the only user of
dcerpc_bind_auth. And this was not only passwords anyway.

Andrew Bartlett, as usual: Please take a close look.

Thanks,

Volker
(This used to be commit 2ff2dae3d035af6cb0c131573cfd983fc9a58eee)