Rename wal_log_hintbits to wal_log_hints, per discussion on pgsql-hackers.

doc/src/sgml/config.sgml

src/backend/access/heap/visibilitymap.c

src/backend/access/transam/xlog.c

src/backend/utils/misc/guc.c

src/backend/utils/misc/postgresql.conf.sample

src/bin/pg_controldata/pg_controldata.c

src/bin/pg_resetxlog/pg_resetxlog.c

src/include/access/xlog.h

src/include/access/xlog_internal.h

src/include/catalog/pg_control.h