Restructure indexscan API (index_beginscan, index_getnext) per
Tom Lane <tgl@sss.pgh.pa.us>
Restructure indexscan API (index_beginscan, index_getnext) per yesterday's proposal to pghackers. Also remove unnecessary parameters to heap_beginscan, heap_rescan. I modified pg_proc.h to reflect the new numbers of parameters for the AM interface routines, but did not force an initdb because nothing actually looks at those fields.