patch adding %afterdecls C code section

The attached patch allows to insert a C code section (in the .c file)
between the declarations and the method implementations, eg:

        %afterdecls{

        static const struct
        {
                void (*one) (Self *self);
                void (*two) (Self *self);
        } things[] = {
          { self_foo, self_bar },
        };

        %}

        class Foo:Bar
        {
                private void
                foo (self)
                {
                }

                private void
                bar (self)
                {
                }
        }

Without this patch, one has to make methods protected if he wants to
refer to them from the %{} code section.

Or, alternatively, put things[] in a %{} section at the end of the
file:

        %{
        typedef struct
        {
                void (*one) (FooBar *self);
                void (*two) (FooBar *self);
        } Thing;

        static const Thing things[];
        %}

        class Foo:Bar
        {
                ...
        }

        %{
        static const Thing things[] = {
                ...
        };
        %}

But it's more verbose and forbids code such as:

        G_N_ELEMENTS(things)

since things[] is not yet defined in the class code.

-- 
Jean-Yves Lefort <jylefort_at_brutele.be>