Serpent: Redundant btyecode

I created these two contracts as examples.
root.se

```
extern child.se: [double:[int256]:int256]

c = create('child.se')
c1 = create('child.se')
c2 = create('child.se')

def call():
    return(c.double(3))
```

and child.se

```
def double(x):
    return(x**2)
```

When `root.se` is compiled, redundant bytecode of the `child.se` is pasted into it instead of just once. Why is that?
