More useful debug messages for custom action/auth functions on startup

Instead of this:
```
2013-11-27 12:43:50,007 DEBUG [ckan.logic] Auth function 'datastore' was inserted
2013-11-27 12:43:50,007 DEBUG [ckan.logic] Auth function 'datastore' was inserted
```
get this:

```
2013-11-27 12:29:12,886 DEBUG [ckan.logic] Action function datastore_create from plugin datastore was inserted
2013-11-27 12:29:12,886 DEBUG [ckan.logic] Action function datastore_make_public from plugin datastore was inserted
```