Fix several completion bugs

[technomancy]

While debugging a new version of Jeejah, I encountered several bugs in Monroe's completion logic.

• The completions request was missing the session field, which all messages should have.
• The monroe-completion-at-point function was using cdadr to extract the "candidate" field instead of actually looking for the completion by name. This probably worked on whatever server it was originally tested with, but it would fail as soon as the response had a different number of fields from that.
• The add-hook call for monroe-completion-at-point was not correctly making the hook changes buffer-local.

However, even after fixing these bugs, I've been unable to get completion working. I've confirmed that responses come back over nrepl like such:

{:completions [{:candidate "tail!" :type "unknown"} {:candidate "table" :type "unknown"}]
 :id "1"
 :ns ">"
 :session "459523637"
 :status ["done"]}

but Monroe still does not correctly show or insert candidates returned by the server. Not sure what's going on there.

[sanel]

Can you try pls with [1] version? I've merged couple of patches before, mostly related to multiple connection support and weird things happens from time to time. I'm loosing content with the last master (no evaluations) and it's a bit hard to debug, so I was planning to revert stuff to [1] and apply other patches done in the mean time. Thoughts?

[1] 508f5ed