Float to int conversion when stringifying and parsing Json.

The json resulting from pretty printing a float value that is exactly an integer doesn't include any period. As a result, when parsing the json again, the same value is interpreted as an integer.

The following example illustrate the problem, but does not involve json pretty-printing or parsing.
```
class Main {
static function main() {
var v : Float = 1.0;
trace(v);
}
}
```

It would be convenient if the pretty-printer used when stringifying json always included a float signifier.