Wrong identifier

Hi,

`sum(price)=gt=3` query generates following object:

``` js
{
name: 'and',
args: [
{ name: 'sumgt', args: [ [ 'price' ], 3 ] }
],
cache: {}
}
```

Shouldn't it be like `gt(sum(price),3)`

``` js
{
name: 'and',
args: [{
name: 'gt',
args: [ { name: 'sum', args: [ 'price' ] }, 3 ]
} ],
cache: {}
}
```

Or at least it may throw exception.

Best Regards,