Local environment is disregarded

[vemv]

The following code will succeed:

(def f inc)

(let [f 2]
  (implement {} some/protocol f))

...but that's counterintuitive. Under the covers, the f local shadows #'f, but the latter is the one that actually gets used.

Ideally, an exception would be thrown if f shadowed an #'f, because it is not intended usage to pass let bindings to implement.