The attached patch converts all function return type hints to spell out the class name fully qualified. There are two reasons for doing this:
1. Simple names in return type hints cause the issue described in http://dev.clojure.org/jira/browse/CLJ-1232. That's usually not a problem with return type hints referring to java.lang-classes because those are always imported. However, using `ns-unmap` you can remove them. For example, after `(ns-unmap ns 'String)` in my namespace, `(.length (format "foo = %s") 1)` throws an IllegalArgumentException: Unable to resolve classname: String. By using fully-qualified class names, that problem goes away.
2. tools.analyzer (used by the Clojure lint tool Eastwood) crashes when encountering such a simple-named return type hint. So currently, I cannot lint parts of my project because there's code that calls `clojure.core/format`.