Fixing this bug took me days. So much hate.

* The Clojure REPL macroexpansion looked eminently reasonable.
* I seem to remember adding a cljs-6502.addressing/ prefix without success.
* The traceback from attempted compilation was COMPLETELY useless,
  stating that
```
clojure.lang.ExceptionInfo: Assert failed: set! target must be a field
  or a symbol naming a var
targetexpr at line 13, etc etc
```
  even though neither the macro nor calling code use `set!` directly.
Minor addressing fixes.