Add regression test for NullPointerException

The new test is similar to NullPointerException2. It checks that a
NullPointerException is correctly caught if the catch block specifies
one of its superclasses.

regression/cbmc-java/NullPointerException4/Test.java

@@ -0,0 +1,15 @@
+class A {
+    int i;
+}
+
+public class Test {
+    public static void main(String args[]) {
+        A a=null;
+        try {
+            a.i=0;
+        }
+        catch (Exception exc) {
+            assert false;
+        }
+    }
+}

regression/cbmc-java/NullPointerException4/java/lang/NullPointerException.java

@@ -0,0 +1,4 @@
+package java.lang;
+
+public class NullPointerException extends RuntimeException {
+}

regression/cbmc-java/NullPointerException4/java/lang/RuntimeException.java

@@ -0,0 +1,4 @@
+package java.lang;
+
+public class RuntimeException extends Exception {
+}

regression/cbmc-java/NullPointerException4/test.desc

@@ -0,0 +1,9 @@
+CORE
+Test.class
+--java-throw-runtime-exceptions
+^EXIT=10$
+^SIGNAL=0$
+^.*assertion at file Test.java line 12 function.*: FAILURE$
+^VERIFICATION FAILED$
+--
+^warning: ignoring