Incorrect rewriting of ENCAPSED strings

This code is rewritten incorrectly:
``` 'json_encode'];
echo "json is {$arr['json_encode']($arr)}\n";
```

Result:
``` 'json_encode'];
echo "json is {\Badoo\SoftMocks::callFunction(__NAMESPACE__, $arr['json_encode'], array(&$arr))}\n";
````

Start by reproducing the provided PHP example and trace the rewriting path for ENCAPSED strings. Compare the generated output with the original callable array access; done means the expression is rewritten into valid PHP without changing its intended lookup or invocation.

Written by the indexing model from the issue text.