add validity check for JSONObject constructors

* fixes #713
* document JSONException in JavaDoc
* remove unused Comparable<T> boundary to reuse GenericBean in test

src/test/java/org/json/junit/data/GenericBean.java

@@ -9,7 +9,7 @@ import java.io.StringReader;
  * @param <T>
  *            generic number value
  */
-public class GenericBean<T extends Number & Comparable<T>> implements MyBean {
+public class GenericBean<T extends Number> implements MyBean {
     /**
      * @param genericValue
      *            value to initiate with