Schema checking option for LDAP Sync replication

doc/man/man5/slapd.conf.5

servers/slapd/config.c

servers/slapd/modify.c

servers/slapd/slap.h

servers/slapd/syncrepl.c

tests/data/slapd-syncrepl-slave-persist1.conf

tests/data/slapd-syncrepl-slave-persist2.conf

tests/data/slapd-syncrepl-slave-persist3.conf

tests/data/slapd-syncrepl-slave-refresh1.conf

tests/data/slapd-syncrepl-slave-refresh2.conf