Corrected link in Javadoc.

core/src/main/java/org/acegisecurity/userdetails/UserDetails.java

@@ -31,7 +31,8 @@ import java.io.Serializable;
  * 
  * <P>
  * Concrete implementations must take particular care to ensure the non-null
- * contract detailed for each method is enforced. See {@link User} for a
+ * contract detailed for each method is enforced. See
+ * {@link net.sf.acegisecurity.providers.dao.User} for a
  * reference implementation (which you might like to extend).
  * </p>
  *