Returns one of the following values:
0 if the entry complies with the schema or if schema checking is turned off. The function also returns 0 if the entry has additional attributes not allowed by the schema and has the object class extensibleObject.
1 if the entry is missing the objectclass attribute, if it is missing any required attributes, if it has any attributes not allowed by the schema (but does not have the object class extensibleObject ), or if the entry has multiple values for a single-valued attribute.