M_EXTCOPYFLAGS
(n)->m_flags |= ((o)->m_flags & M_EXTCOPYFLAGS); \
m->m_flags = (m->m_flags & ~M_EXTCOPYFLAGS) |
(m)->m_flags = ((m)->m_flags & ~M_EXTCOPYFLAGS) | \
(m)->m_flags = ((m)->m_flags & ~M_EXTCOPYFLAGS) | M_EXT; \