Silence compiler warnings on XML classes for lack of Serializable version.

core/src/processing/xml/XMLElement.java

@@ -47,6 +47,7 @@ import processing.core.PApplet;
  * @usage Web & Application
  * @instanceName xml any variable of type XMLElement
  */
+@SuppressWarnings("serial")
 public class XMLElement implements Serializable {
   /** No line number defined. */
   public static final int NO_LINE = -1;

core/src/processing/xml/XMLException.java

@@ -39,6 +39,7 @@ import java.io.PrintWriter;
  * @author Marc De Scheemaecker
  * @version $Name: RELEASE_2_2_1 $, $Revision: 1.4 $
  */
+@SuppressWarnings("serial")
 public class XMLException
    extends Exception
 {

core/src/processing/xml/XMLParseException.java

@@ -36,6 +36,7 @@ package processing.xml;
  * @author Marc De Scheemaecker
  * @version $Name: RELEASE_2_2_1 $, $Revision: 1.3 $
  */
+@SuppressWarnings("serial")
 public class XMLParseException
    extends XMLException
 {

core/src/processing/xml/XMLValidationException.java

@@ -36,6 +36,7 @@ package processing.xml;
  * @author Marc De Scheemaecker
  * @version $Name: RELEASE_2_2_1 $, $Revision: 1.3 $
  */
+@SuppressWarnings("serial")
 public class XMLValidationException
    extends XMLException
 {