r7633: this patch started as an attempt to make the dcerpc code use a given

r7633: this patch started as an attempt to make the dcerpc code use a given
event_context for the socket_connect() call, so that when things that
use dcerpc are running alongside anything else it doesn't block the
whole process during a connect.

Then of course I needed to change any code that created a dcerpc
connection (such as the auth code) to also take an event context, and
anything that called that and so on .... thus the size of the patch.

There were 3 places where I punted:

  - abartlet wanted me to add a gensec_set_event_context() call
    instead of adding it to the gensec init calls. Andrew, my
    apologies for not doing this. I didn't do it as adding a new
    parameter allowed me to catch all the callers with the
    compiler. Now that its done, we could go back and use
    gensec_set_event_context()

  - the ejs code calls auth initialisation, which means it should pass
    in the event context from the web server. I punted on that. Needs fixing.

  - I used a NULL event context in dcom_get_pipe(). This is equivalent
    to what we did already, but should be fixed to use a callers event
    context. Jelmer, can you think of a clean way to do that?

I also cleaned up a couple of things:

 - libnet_context_destroy() makes no sense. I removed it.

 - removed some unused vars in various places
(This used to be commit 3a3025485bdb8f600ab528c0b4b4eef0c65e3fc9)