scroll_t
int vs_sm_scroll(SCR *, MARK *, recno_t, scroll_t);
static int vs_sm_down(SCR *, MARK *, recno_t, scroll_t, SMAP *);
static int vs_sm_up(SCR *, MARK *, recno_t, scroll_t, SMAP *);
vs_sm_scroll(SCR *sp, MARK *rp, recno_t count, scroll_t scmd)
vs_sm_up(SCR *sp, MARK *rp, recno_t count, scroll_t scmd, SMAP *smp)
vs_sm_down(SCR *sp, MARK *rp, recno_t count, scroll_t scmd, SMAP *smp)