Allow getting id of cell objects

Author: msimacek

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/object/ObjectNodes.java

@@ -82,6 +82,7 @@
 import com.oracle.graal.python.builtins.objects.PNone;
 import com.oracle.graal.python.builtins.objects.PNotImplemented;
 import com.oracle.graal.python.builtins.objects.bytes.PBytes;
+import com.oracle.graal.python.builtins.objects.cell.PCell;
 import com.oracle.graal.python.builtins.objects.cext.PythonAbstractNativeObject;
 import com.oracle.graal.python.builtins.objects.cext.PythonNativeVoidPtr;
 import com.oracle.graal.python.builtins.objects.cext.capi.CExtNodes;
@@ -369,6 +370,11 @@ Object id(PythonNativeVoidPtr self) {
             return self.getNativePointer();
         }
 
+        @Specialization
+        Object id(PCell self) {
+            return PythonContext.get(this).getNextObjectId(self);
+        }
+
         protected static boolean isDefaultCase(PythonObject object) {
             return !(object instanceof PBytes ||
                             object instanceof PFrozenSet ||