:unused-namespaces should also check for (resolve 'some.namespace/foo)

Currently, the `:unused-namespaces` linter reports false positives on code like

```
(require 'some.namespace)
(let [foo (resolve 'some.namespace/foo)]
  ...)
```

The above is quite common, especially if you have circular dependencies i think.

I don't think it would be too much work to find all namespaces used in `clojure.core/resolve` calls and include them in the set of used namespaces.
