Failure to parse protected inner struct of class Logger in std.experimental.core

Auto-complete doesn't show any fields of `payload` in this code:

``` D
import std.experimental.logger;

class FunkyLogger : Logger
{
    this(LogLevel lv)
    {
        super(lv);
    }

    override void writeLogMsg(ref LogEntry payload)
    {
        payload.|
    }
}
```
