[log] Add "Create Patch" action

Reuse CreatePatchFromChangesAction with update() method overridden in
the same matter, as it is done for GitLogUi: to respect the CHANGES
data key.

platform/vcs-log/impl/src/META-INF/vcs-log.xml

@@ -17,6 +17,7 @@
   <actions>
     <action class="com.intellij.vcs.log.ui.VcsLogCopyHashAction" id="Vcs.Log.CopyHash"
             icon="AllIcons.Actions.Copy" text="Copy Hash" description="Copy hash value of the selected commit to clipboard" />
+    <action class="com.intellij.vcs.log.ui.VcsLogCreatePatchAction" id="Vcs.Log.CreatePatch" />
     <action class="com.intellij.vcs.log.ui.VcsLogQuickSettingsActions" id="Vcs.Log.QuickSettings"
             icon="AllIcons.General.Gear" text="Quick Settings" description="Quick Settings" />
     
@@ -26,6 +27,7 @@
     </group>
     <group id="Vcs.Log.ContextMenu">
       <reference id="Vcs.Log.CopyHash"/>
+      <reference id="Vcs.Log.CreatePatch"/>
     </group>
   </actions>
 

platform/vcs-log/impl/src/com/intellij/vcs/log/ui/VcsLogCreatePatchAction.java

@@ -0,0 +1,31 @@
+/*
+ * Copyright 2000-2013 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.intellij.vcs.log.ui;
+
+import com.intellij.openapi.actionSystem.AnActionEvent;
+import com.intellij.openapi.vcs.VcsDataKeys;
+import com.intellij.openapi.vcs.changes.Change;
+import com.intellij.openapi.vcs.changes.actions.CreatePatchFromChangesAction;
+
+public class VcsLogCreatePatchAction extends CreatePatchFromChangesAction {
+
+  @Override
+  public void update(AnActionEvent e) {
+    Change[] changes;
+    e.getPresentation().setEnabled((changes = e.getData(VcsDataKeys.CHANGES)) != null && changes.length > 0);
+  }
+
+}