add a few classes and methods to the classpath

Add java.lang.CharSequence, java.util.AbstractSet,
java.util.AbstractCollection, Collections.unmodifiableSet,
 System.getProperty(String,String), etc.

classpath/java/lang/Class.java

@@ -415,4 +415,8 @@ public final class Class <T> {
       return null;
     }
   }
+  
+  public boolean desiredAssertionStatus() {
+	  return false;
+  }
 }