Do not follow href after sending POST via l:task

Simple `<l:task post="true" href="someurl"/>` triggers post request as expected
but then proceeds to href as normal link to. If the URL accepts GET then request
is sent twice it if does not after POSTing on background user get
'POST is required' error.

core/src/main/resources/lib/layout/task.jelly

@@ -207,7 +207,7 @@ THE SOFTWARE.
               </l:confirmationLink>
             </j:when>
             <j:otherwise>
-              <a href="${href}" class="task-link" onclick="${attrs.onclick ?: (post ? 'postRequest_' + id + '(this)' : null)}">
+              <a href="${href}" class="task-link" onclick="${attrs.onclick ?: (post ? 'return postRequest_' + id + '(this)' : null)}">
                 <j:choose>
                   <j:when test="${match}">
                     <b>${title}</b>

test/src/test/java/lib/layout/TaskTest.java

+/*
+ * The MIT License
+ *
+ * Copyright (c) 2015 Red Hat, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package lib.layout;
+
+import static org.junit.Assert.assertTrue;
+
+import java.io.IOException;
+
+import javax.servlet.ServletException;
+
+import hudson.model.UnprotectedRootAction;
+
+import org.junit.Rule;
+import org.junit.Test;
+import org.jvnet.hudson.test.JenkinsRule;
+import org.jvnet.hudson.test.JenkinsRule.WebClient;
+import org.jvnet.hudson.test.TestExtension;
+import org.kohsuke.stapler.StaplerRequest;
+import org.kohsuke.stapler.StaplerResponse;
+import org.kohsuke.stapler.interceptor.RequirePOST;
+
+import com.gargoylesoftware.htmlunit.html.HtmlPage;
+
+public class TaskTest {
+
+    @Rule public JenkinsRule j = new JenkinsRule();
+
+    @Test public void postLink() throws Exception {
+        WebClient wc = j.createWebClient();
+        HtmlPage page = wc.goTo(postLink.getUrlName());
+        page.getAnchorByText("POST").click();
+        assertTrue("Action method should be invoked", postLink.called);
+    }
+
+    @TestExtension("postLink") public static final MockAction postLink = new MockAction();
+    public static class MockAction implements UnprotectedRootAction {
+        private boolean called = false;
+        @RequirePOST public void doPost(StaplerRequest req, StaplerResponse rsp) throws ServletException, IOException {
+            if (called) throw new AssertionError();
+            called = true;
+            rsp.forwardToPreviousPage(req);
+        }
+
+        public String getIconFileName() {
+            return null;
+        }
+
+        public String getDisplayName() {
+            return null;
+        }
+
+        public String getUrlName() {
+            return "post-link";
+        }
+    }
+}

test/src/test/resources/lib/layout/TaskTest/MockAction/index.jelly

+<!--
+The MIT License
+
+Copyright (c) 2015, Red Hat, Inc.
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
+-->
+
+<?jelly escape-by-default='true'?>
+<j:jelly xmlns:j="jelly:core" xmlns:st="jelly:stapler" xmlns:d="jelly:define" xmlns:l="/lib/layout" xmlns:t="/lib/hudson" xmlns:f="/lib/form">
+  <l:layout title="">
+    <l:main-panel>
+      <l:task href="post" title="POST" post="true"/>
+    </l:main-panel>
+  </l:layout>
+</j:jelly>