Smart padding when pasting code

Right, when pasting multiline code, the padding between the code and the evaluation result is adjusted. But it is not done when pasting a simple string without new line.

From

``` scala
prinln("hello")        //> hello
```

Pasting `world` result in

``` scala
println("hello world")        //> hello
```

It should become

``` scala
println("hello world")  //> hello
```
