State checking for extending abstract classes

使用 URLConnectionRefinements 注解、URLExt 和 Testurl 示例重现该报告。首先跟踪在 URLExt 上调用方法时，如何检查从 java.net.URLConnection 继承的状态细化。完成的标准是：setDoInput(false) 被接受，而 getContent() 被拒绝，因为对象尚未达到已连接状态。

Currently, reusing state refinements from an abstract superclass in a concrete class is not fully implemented, and gives an error like the one below.

Example for abstract class java.net.URLConnection:

@ExternalRefinementsFor("java.net.URLConnection")
@StateSet({"setup", "connected"})
public interface URLConnectionRefinements {
 
    @StateRefinement(to="setup(this)")
    public void URLConnection(URL url);

    @StateRefinement(from="setup(this)")
    public void setDoInput(boolean doinput);

    @StateRefinement(from="setup(this)", to="connected(this)")
    public void connect();

    @StateRefinement(from="connected(this)")
    public Object getContent();
 
}

Extended in class URLExt:

class URLExt extends URLConnection{

    public URLExt(URL url){
        super(url);
    }

    @Override
    public void connect() throws IOException {
        // TODO Auto-generated method stub
        throw new UnsupportedOperationException("Unimplemented method 'connect'");
    }
    
}```

Tested in:
```java
class Testurl {
    void test() throws URISyntaxException, IOException {

        URLExt u = new URLExt(new URI("http://example.com").toURL());
        u.setDoInput(false); // should not be an error but it is 
        u.getContent(); // should be an error

    }
}