Expand arguments to React DOM fns in interpreter.

The sablono compiler correctly splices in arguments to React DOM fns, but whenever >1 arguments are present, the interpreter passes them as an array rather than normal arguments. This triggers the [React dynamic children warning](http://facebook.github.io/react/docs/multiple-components.html#dynamic-children), even with static children, such as in the form `[:div [:div] [:div]]`.

Minimal example repo [here](https://github.com/jenanwise/sablono-interp-test/blob/master/src/sablono_interp_test/core.cljs). Note that under React 0.9.0, the first render *won't* trigger the warning. See comments in the example repo.

### Existing behavior detail

Under the current master, sablono takes the following:

```clojure
;; compiled
(html [:div [:div] [:div]])
```

and compiles it down to:

```js
React.DOM.div(null, React.DOM.div(null), React.DOM.div(null))
```

However, if you force sablono to use its interpreter (such as by wrapping the markup in a bare `(let)`), sablono will call React with a single array of children rather than positional arguments. E.g.,

```clojure
;; interpreted
(html (let [] [:div [:div] [:div]]))
```

results in a call that looks like

```js
React.DOM.div(null, [React.DOM.div(null), React.DOM.div(null)])
```

This produces the same output as the compiled version, but triggers React's dynamic children warning.

You can see this difference in the [compiler code](https://github.com/r0man/sablono/blob/0338ca029df050fcecf2ce9db0522560a9ee5340/src/sablono/compiler.clj#L74), which splices in positional arguments, and the [interpreter code](https://github.com/r0man/sablono/blob/0338ca029df050fcecf2ce9db0522560a9ee5340/src/sablono/interpreter.cljx#L73), which does not splice and which does not currently use `(apply)`.

### Changes

This patch modifies the interpreter code to use `(apply)`, forcing the children elements to be positional arguments to the React DOM function and matching behavior of the compiler.

### Testing

Since output for positional vs array of children arguments to React DOM functions is identical, I added an interpreter test helper that throws when encountering array arguments to the React DOM fns returned by sablono's `(dom-fn)`. All other existing tests pass.