Monkeypatch cover.log while intializing nosexcover so that log messages say nose.plugins.xcover instead of nose.plugins.cover

This is on the hacky side...

Maybe it's just me, but I've been irritated for a while by the fact that when I run nosetests, it outputs the same log message twice:

```
nose.plugins.cover: INFO: Coverage report will include only packages: ['profilesvc']
nose.plugins.cover: INFO: Coverage report will include only packages: ['profilesvc']
```

This made me wonder whether I had some bug in my configuration or if there was a bug in the cover plugin.

I finally looked at it tonight and I realized that this happens because nosexcover inherits from nosecover and calls its `configure` method, so nosecover's `configure` gets called once my `nosexcover` and once by the nose plugin manager.

My attempt at making it at least clearer what's happening was this PR which does a little bit of monkeypatching so that one log message says `nose.plugins.cover` and one says `nose.plugins.xcover` -- at least that makes it a little more clear why the message is printed twice.

Not sure this is a ton better, but maybe this will spark some more ideas on how to deal with the situation.