First-cut proxy authorization support.

clients/tools/ldapcompare.c

clients/tools/ldapdelete.c

clients/tools/ldapmodify.c

clients/tools/ldapmodrdn.c

clients/tools/ldappasswd.c

clients/tools/ldapsearch.c

clients/tools/ldapwhoami.c

include/ldap.h

libraries/libldap/error.c

servers/slapd/config.c

servers/slapd/controls.c

servers/slapd/extended.c

servers/slapd/proto-slap.h

servers/slapd/result.c

servers/slapd/sasl.c

servers/slapd/saslauthz.c

servers/slapd/slap.h

servers/slapd/tools/mimic.c

tests/scripts/test014-whoami