More include file cleanups

src/backend/access/gist/giststrat.c

src/backend/access/heap/hio.c

src/backend/access/index/indexam.c

src/backend/access/index/istrat.c

src/backend/access/nbtree/nbtcompare.c

src/backend/access/nbtree/nbtpage.c

src/backend/access/nbtree/nbtree.c

src/backend/access/nbtree/nbtscan.c

src/backend/access/nbtree/nbtsearch.c

src/backend/access/nbtree/nbtsort.c

src/backend/access/nbtree/nbtstrat.c

src/backend/access/nbtree/nbtutils.c

src/backend/access/rtree/rtget.c

src/backend/access/rtree/rtree.c

src/backend/access/rtree/rtscan.c

src/backend/access/rtree/rtstrat.c

src/backend/access/transam/transam.c

src/backend/access/transam/transsup.c

src/backend/access/transam/varsup.c

src/backend/access/transam/xact.c