minor naming cleanup; improvements to DN mapping layer; major docs update

doc/man/man5/slapd-sql.5

servers/slapd/back-sql/add.c

servers/slapd/back-sql/api.c

servers/slapd/back-sql/back-sql.h

servers/slapd/back-sql/bind.c

servers/slapd/back-sql/config.c

servers/slapd/back-sql/delete.c

servers/slapd/back-sql/init.c

servers/slapd/back-sql/modrdn.c

servers/slapd/back-sql/proto-sql.h

servers/slapd/back-sql/rdbms_depend/ibmdb2/slapd.conf

servers/slapd/back-sql/rdbms_depend/mysql/slapd.conf

servers/slapd/back-sql/rdbms_depend/oracle/slapd.conf

servers/slapd/back-sql/rdbms_depend/pgsql/slapd.conf

servers/slapd/back-sql/rdbms_depend/timesten/slapd.conf

servers/slapd/back-sql/search.c

servers/slapd/back-sql/util.c