patch adding first-class support of constructor/dispose/finalize methods

The attached patch allows to write:

        constructor (self)
        {
                /* hi */
        }

        dispose (self)
        {
                /* hi */
        }

        finalize (self)
        {
                /* hi */
        }

instead of:

        override (G:Object) GObject *
        constructor (GType type, unsigned int n_construct_properties, GObjectConstructParam *construct_params)
        {
                GObject *object;
                Self *self;

                object = PARENT_HANDLER(type, n_construct_properties, construct_params);
                self = SELF(object);

                /* hi */

                return object;
        }

        override (G:Object) void
        dispose (GObject *object)
        {
                Self *self = SELF(object);

                /* hi */

                PARENT_HANDLER(object);
        }

        override (G:Object) void
        finalize (GObject *object)
        {
                Self *self = SELF(object);

                /* hi */

                PARENT_HANDLER(object);
        }

In my opinion, these virtual methods are used so often that they
deserve such first-class support.

Of course, to preserve backwards compatibility, the normal override
syntax is still supported.

-- 
Jean-Yves Lefort <jylefort_at_brutele.be>