Fix some style and react key problems

components/tabs/demo/new-and-close.md

@@ -20,9 +20,9 @@ function newTabPane() {
 
 ReactDOM.render(
   <Tabs onChange={callback} type="card" editable newTabPane={newTabPane}>
-    <TabPane tab="卡一" key="1">选项卡一内容</TabPane>
-    <TabPane tab="卡二" key="2">选项卡二内容</TabPane>
-    <TabPane tab="卡三" key="3">选项卡三内容</TabPane>
+    <TabPane tab="选项卡" key="1">选项卡一内容</TabPane>
+    <TabPane tab="选项卡" key="2">选项卡二内容</TabPane>
+    <TabPane tab="选项卡" key="3">选项卡三内容</TabPane>
   </Tabs>
 , document.getElementById('components-tabs-demo-new-and-close'));
 ````

components/tabs/index.jsx

@@ -53,7 +53,9 @@ class AntTabs extends React.Component {
       }
     });
     if (activeKey === key) {
-      activeKey = tabs[foundIndex - 1].key;
+      foundIndex = foundIndex - 1;
+      foundIndex = foundIndex >= 0 ? foundIndex : 0;
+      activeKey = tabs[foundIndex].key;
     }
     this.setState({
       tabs,
@@ -94,10 +96,10 @@ class AntTabs extends React.Component {
         children = this.state.tabs;
       }
       // Add new tab handler
-      tabBarExtraContent = [
-        <Icon type="plus" className={prefixCls + '-new-tab'} onClick={this.createNewTab} />,
-        tabBarExtraContent,
-      ];
+      tabBarExtraContent = <span>
+        <Icon type="plus" className={prefixCls + '-new-tab'} onClick={this.createNewTab} />
+        {tabBarExtraContent}
+      </span>;
     }
     // Wrap the extra content
     tabBarExtraContent = <div className={prefixCls + '-extra-content'}>

style/components/tabs.less

@@ -397,6 +397,7 @@
     margin-right: 0;
     margin-left: 4px;
     font-size: 12px;
+    width: 12px;
     color: #999;
     transition: color 0.3s ease;
     &:hover {
@@ -417,6 +418,7 @@
       border-radius: 3px;
       border: 1px solid @border-color-base;
       font-size: 12px;
+      .iconfont-size-under-12px(10px);
       transition: color 0.3s ease;
       &:hover {
         color: @primary-color;