Fix compile statement return object.

Results should not have a "status" field. It leads to return objects such as:
```
{
  "result" : {
               "kind" : "std exception",
               "msg" : "Cannot allocate memory",
               "status" : "error"
             },
  "status":"ok"
}
```
This PR fixes it so that we end up with:
```
{
  "result" : "Cannot allocate memory",
  "status" : "error"
}
```
Well, `TSourceError` is only thrown by `Compile` so I'm not sure it's better that we catch it at a higher level.