401211 - Remove requirement for jetty-websocket.jar in WEB-INF/lib

+ Adding appropriate configuration in WebAppContext to use
    WebSocketServlet from server classloader.  Similar to how
    the WebSocket interface and WebSocketFactory are also
    defined.
  + Marking jetty-websocket as provided in test webapp

jetty-webapp/src/main/java/org/eclipse/jetty/webapp/WebAppContext.java

@@ -109,6 +109,7 @@ public class WebAppContext extends ServletContextHandler implements WebAppClassL
         "org.eclipse.jetty.plus.jaas.",     // webapp cannot change jaas classes
         "org.eclipse.jetty.websocket.WebSocket", // WebSocket is a jetty extension
         "org.eclipse.jetty.websocket.WebSocketFactory", // WebSocket is a jetty extension
+        "org.eclipse.jetty.websocket.WebSocketServlet", // webapp cannot change WebSocketServlet
         "org.eclipse.jetty.servlet.DefaultServlet" // webapp cannot change default servlets
     } ;
 
@@ -123,6 +124,7 @@ public class WebAppContext extends ServletContextHandler implements WebAppClassL
         "-org.eclipse.jetty.plus.jaas.",    // don't hide jaas classes
         "-org.eclipse.jetty.websocket.WebSocket", // WebSocket is a jetty extension
         "-org.eclipse.jetty.websocket.WebSocketFactory", // WebSocket is a jetty extension
+        "-org.eclipse.jetty.websocket.WebSocketServlet", // don't hide WebSocketServlet
         "-org.eclipse.jetty.servlet.DefaultServlet", // don't hide default servlet
         "-org.eclipse.jetty.servlet.listener.", // don't hide useful listeners
         "org.eclipse.jetty."                // hide other jetty classes

test-jetty-webapp/pom.xml

@@ -176,7 +176,7 @@
       <groupId>org.eclipse.jetty</groupId>
       <artifactId>jetty-websocket</artifactId>
       <version>${project.version}</version>
-      <!--scope>provided</scope-->
+      <scope>provided</scope>
     </dependency>
     <dependency>
       <groupId>org.eclipse.jetty</groupId>