Add wxObjectDataPtr::release()

This makes it possible to use wxObjectDataPtr inside functions returning
raw pointers owned by the caller, such as custom GetAttr() in the grid
sample.

interface/wx/object.h

@@ -608,6 +608,21 @@ public:
     */
     void reset(T *ptr);
 
+    /**
+        Release the owned pointer, making caller responsible for decrementing
+        its reference count.
+
+        This method should be used only for interoperating with the existing
+        code working with raw pointers, typically when returning a raw pointer
+        from a function.
+
+        After calling this function, this object becomes invalid, i.e. it
+        doesn't hold any valid pointer value any more.
+
+        @since 3.1.4
+    */
+    T* release();
+
     /**
         Conversion to a boolean expression (in a variant which is not
         convertable to anything but a boolean expression).