hy/lex/parser.py: Mungle (.foo? bar) a bit better

I have a class, to which I want to add an `is_foo` function, and would like to be able to call it from Hy like `(.foo? bar)`, this patch makes that possible in a very crude way. Don't even think about merging it, there are no tests either. But I wanted to have the patch here with the issue, just in case.

Anyway, this is a sample code I'd love to have supported:

```clojure
(defclass Foo [object]
  [[foo? (fn [_] true)]])

(.foo? (Foo)) ;; => true
```