Use a valid url-pattern

Tomcat 6 complaints about the url pattern. Changes on it were done for
doing some workarounds in ZK5 support, but it doesn't seem necessary.

FEA: ItEr75S04BugFixing

navalplanner-webapp/src/main/webapp/WEB-INF/web.xml

@@ -38,7 +38,7 @@
     </servlet>
     <servlet-mapping>
         <servlet-name>callbackServlet</servlet-name>
-        <url-pattern>callback/*</url-pattern>
+        <url-pattern>/callback/*</url-pattern>
     </servlet-mapping>
     <servlet-mapping>
         <servlet-name>dspLoader</servlet-name>