slapi-plugin.h now includes ldap_msg.h, which lists unique error numbers used by Directory Server.
Functions for dealing with back ends that return int error codes can now also return SLAPI_FAIL_RETRY. The old values are also still used.
Directory Server now distinguishes between two results. SLAPI_BIND_FAIL indicates that the bind failed and the server prepared a result to send. SLAPI_BIND_ANONYMOUS indicates that the bind succeeded as an anonymous bind.