[FIXED JENKINS-12945] absolutize links in the context menu

Absolutizing on the server side is easier and more compact.

changelog.html

@@ -55,6 +55,9 @@ Upcoming changes</a>
 <!-- Record your changes in the trunk here. -->
 <div id="trunk" style="display:none"><!--=TRUNK-BEGIN=-->
 <ul class=image>
+  <li class=bug>
+    Some of the context menu items have wrong links
+    (<a href="https://issues.jenkins-ci.org/browse/JENKINS-12945">issue 12945</a>)
   <li class=rfe>
     Performance improvement in JavaScript on modern browsers
     (<a href="https://github.com/jenkinsci/jenkins/pull/276">pull 276</a>)

core/src/main/java/jenkins/model/ModelObjectWithContextMenu.java

@@ -24,6 +24,7 @@ import org.xml.sax.helpers.DefaultHandler;
 
 import javax.servlet.ServletException;
 import java.io.IOException;
+import java.net.URI;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
@@ -163,7 +164,7 @@ public interface ModelObjectWithContextMenu extends ModelObject {
         public String icon;
 
         public MenuItem(String url, String icon, String displayName) {
-            this.url = url;
+            this.url = URI.create(Stapler.getCurrentRequest().getRequestURI()).resolve(url).toString();
             this.icon = icon;
             this.displayName = Util.escape(displayName);
         }