major namespace cleanup & minor fixes

servers/slapd/back-meta/add.c

servers/slapd/back-meta/attribute.c

servers/slapd/back-meta/back-meta.h

servers/slapd/back-meta/bind.c

servers/slapd/back-meta/candidates.c

servers/slapd/back-meta/compare.c

servers/slapd/back-meta/config.c

servers/slapd/back-meta/conn.c

servers/slapd/back-meta/delete.c

servers/slapd/back-meta/dncache.c

servers/slapd/back-meta/group.c

servers/slapd/back-meta/init.c

servers/slapd/back-meta/modify.c

servers/slapd/back-meta/modrdn.c

servers/slapd/back-meta/search.c

servers/slapd/back-meta/unbind.c