php上传常见文件类型对应的$_FILES["file"]["type"] from:http://hi.baidu.com/7book/item/374971202075408c6e2cc3a4 xlsapplication/vnd.ms-excelxlsxapplication/vnd.openxmlformats-officedocument.spreadsheetml.sheetpptapplication/vnd.ms-powerpointpptxappl