IE9 compatibility

Hi, I'm getting an error on IE9 and it's beyond my javascript knowledge...

```js
SCRIPT438: Object doesn't support property or method 'apply'
log.js, line 22 character 5
```

It points to [log.js#L22](https://github.com/adamschwartz/log/blob/master/log.js#L22).
Any clue on your side ?

Cheers