Add limit prop for upload

components/upload/demo/basic.md

@@ -1,6 +1,6 @@
 # 点击上传
 
-- order: 1
+- order: 0
 
 经典款式，用户点击按钮弹出文件选择框。
 

components/upload/demo/limit.md

@@ -0,0 +1,33 @@
+# 文件列表限制
+
+- order: 3
+
+`limit` 属性控制文件列表数的上限。如设为 1 时，表示只能上传一个文件，新文件会顶掉旧文件。
+
+---
+
+````jsx
+var Upload = antd.Upload;
+
+var props = {
+  description: '支持扩展名为: .rar .zip ...',
+  action: '/upload.do',
+  data: {},
+  accept: '',
+  uploadTip: '',
+  limit: 1,
+  onStart(file){
+    console.log(file.uid);
+  }
+};
+
+React.render(
+  <Upload {...props}>
+    <button className="ant-btn ant-btn-ghost">
+      <i className="anticon anticon-upload"></i> 点击上传，只支持一个文件
+    </button>
+  </Upload>,
+  document.getElementById('components-upload-demo-limit')
+);
+````
+

components/upload/index.jsx

@@ -25,6 +25,9 @@ const AntUpload = React.createClass({
       file: file,
       status: 'downloading'
     });
+    if (nextDownloadList.length === this.props.limit + 1) {
+      nextDownloadList = nextDownloadList.slice(1);
+    }
     this.setState({
       downloadList: nextDownloadList
     });
@@ -84,6 +87,7 @@ const AntUpload = React.createClass({
       onSuccess: noop,
       onProgress: noop,
       onRemove: noop,
+      limit: Number.MAX_VALUE,
       urlResolver: function(ret) {
         try {
           return JSON.parse(ret).url;
@@ -117,7 +121,9 @@ const AntUpload = React.createClass({
               {this.props.children}
             </Upload>
           </div>
-          <UploadList items={this.state.downloadList} onRemove={this.onRemove}/>
+          <UploadList items={this.state.downloadList}
+                      onRemove={this.onRemove}
+                      limit={props.limit} />
         </div>
       );
     }

components/upload/index.md

@@ -29,6 +29,7 @@
 | onSuccess  | 可选参数, success callback                                 | Function     | 无    |
 | onProgress | 可选参数, progress callback, 现代浏览器有效                  | Function     | 无    |
 | urlResolver| 通过解析请求返回数据，获得文件上传的远程地址                 | Function     | `function() { return JSON.parse(ret).url }` |
+| limit      | 文件上传数量的限制                 | Number     | Number.MAX_VALUE |
 
 ### onError