B+Tree Index Pages
Status get_first(RID& rid, void *key, PageId &pageNo)
sets up rid with first record on current page (use curPage value inherited from HFPage)
returns <key,pageNo> (using get_key_data)
should return NOMORERECS if none on page
Status get_next(RID& rid, void *key, PageId &pageNo)
increments slotNo in rid, gets corresponding key,pageNo from resulting record
should return NOMORERECS if none on page