Add missing cache setting

Fix #1650

Author: fredericDelaporte

src/NHibernate/nhibernate-configuration.xsd

@@ -90,6 +90,7 @@
 								<xs:enumeration value="cache.region_prefix" />
 								<xs:enumeration value="cache.use_minimal_puts" />
 								<xs:enumeration value="cache.default_expiration" />
+								<xs:enumeration value="cache.use_sliding_expiration" />
 								<xs:enumeration value="query.substitutions" />
 								<xs:enumeration value="query.factory_class" />
 								<xs:enumeration value="query.linq_provider_class" />