Export method _size for operator GET_SIZE

m-rbtree.h

@@ -61,6 +61,7 @@
    TYPE(M_C(name,_t)),							\
    SUBTYPE(M_C(name, _type_t)),						\
    TEST_EMPTY(M_C(name,_empty_p)),                                      \
+   GET_SIZE(M_C(name, _size)),                                          \
    IT_TYPE(M_C(name, _it_t)),						\
    IT_FIRST(M_C(name,_it)),						\
    IT_SET(M_C(name,_it_set)),						\