Major code cleanups from D'arcy (-Wall -Werror)

src/backend/access/gist/gist.c

src/backend/access/gist/giststrat.c

src/backend/access/hash/hash.c

src/backend/access/hash/hashovfl.c

src/backend/access/index/istrat.c

src/backend/access/nbtree/nbtcompare.c

src/backend/access/nbtree/nbtinsert.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/nbtutils.c

src/backend/access/rtree/rtget.c

src/backend/access/rtree/rtproc.c

src/backend/access/rtree/rtree.c

src/backend/access/rtree/rtscan.c

src/backend/access/transam/transsup.c

src/backend/bootstrap/bootscanner.l

src/backend/bootstrap/bootstrap.c