Cleanup of /include #include's, for 6.6 only.

src/backend/access/hash/hashscan.c

src/backend/access/hash/hashutil.c

src/backend/access/heap/heapam.c

src/backend/access/index/indexam.c

src/backend/access/nbtree/nbtinsert.c

src/backend/access/nbtree/nbtpage.c

src/backend/access/nbtree/nbtscan.c

src/backend/access/nbtree/nbtsearch.c

src/backend/access/nbtree/nbtsort.c

src/backend/access/nbtree/nbtutils.c

src/backend/access/rtree/rtget.c

src/backend/access/rtree/rtproc.c

src/backend/access/rtree/rtscan.c

src/backend/access/transam/xid.c

src/backend/lib/stringinfo.c

src/backend/libpq/crypt.c

src/backend/nodes/list.c

src/backend/nodes/nodes.c

src/backend/optimizer/geqo/geqo_erx.c

src/backend/optimizer/geqo/geqo_params.c