Move most of SLAPI frontend into overlay

servers/slapd/acl.c

servers/slapd/add.c

servers/slapd/backend.c

servers/slapd/bind.c

servers/slapd/compare.c

servers/slapd/connection.c

servers/slapd/delete.c

servers/slapd/extended.c

servers/slapd/frontend.c

servers/slapd/modify.c

servers/slapd/modrdn.c

servers/slapd/operation.c

servers/slapd/overlays/glue.c

servers/slapd/result.c

servers/slapd/search.c

servers/slapd/slap.h

servers/slapd/slapi/Makefile.in

servers/slapd/slapi/plugin.c

servers/slapd/slapi/slapi.h

servers/slapd/slapi/slapi_ops.c