input file控件限制上传文件类型
http://www.th7.cn/web/html-css/201311/14992.shtml
网页上添加一个input file HTML控件：
<input id="File1" type="file" />
默认是这样的，所有文件类型都会显示出来，如果想限制它只显示我们设定的文件类型呢，比如“word“,”excel“,”pdf“文件
解决办法是可以给它添加一个accept属性，比如：
<input id="File1" type="file" accept=".xls,.doc,.txt,.pdf" />
这样选择的时候默认会显示为这样：
文件选择框内只显示出你自定义文件类型的文件，也还比较方便。
But,这只是最简单的掩人耳目的做法，还是能选择其它文件类型：
所以，如果要做到真正意义上限制类型做法（其实这种算不上限制，只是把你要的文件类型默认显示出来而已，并不是说不能选择其它的），还是要通过js或者后台来控制。
附支持的文件类型：
*.3gpp audio/3gpp， video/3gpp 3GPP Audio/Video*.ac3 audio/ac3 AC3 Audio*.asf allpication/vnd.ms-asf Advanced Streaming Format*.au audio/basic AU Audio*.css text/css Cascading Style Sheets*.csv text/csv Comma Separated Values*.doc application/msword MS Word Document*.dot application/msword MS Word Template*.dtd application/xml-dtd Document Type Definition*.dwg image/vnd.dwg AutoCAD Drawing Database*.dxf image/vnd.dxf AutoCAD Drawing Interchange Format*.gif image/gif Graphic Interchange Format*.htm text/html HyperText Markup Language*.html text/html HyperText Markup Language*.jp2 image/jp2 JPEG-2000*.jpe image/jpeg JPEG*.jpeg image/jpeg JPEG*.jpg image/jpeg JPEG*.js text/javascript， application/javascript JavaScript*.json application/json JavaScript Object Notation*.mp2 audio/mpeg， video/mpeg MPEG Audio/Video Stream， Layer II*.mp3 audio/mpeg MPEG Audio Stream， Layer III*.mp4 audio/mp4， video/mp4 MPEG-4 Audio/Video*.mpeg video/mpeg MPEG Video Stream， Layer II*.mpg video/mpeg MPEG Video Stream， Layer II*.mpp application/vnd.ms-project MS Project Project*.ogg application/ogg， audio/ogg Ogg Vorbis*.pdf application/pdf Portable Document Format*.png image/png Portable Network Graphics*.pot application/vnd.ms-powerpoint MS PowerPoint Template*.pps application/vnd.ms-powerpoint MS PowerPoint Slideshow*.ppt application/vnd.ms-powerpoint MS PowerPoint Presentation*.rtf application/rtf， text/rtf Rich Text Format*.svf image/vnd.svf Simple Vector Format*.tif image/tiff Tagged Image Format File*.tiff image/tiff Tagged Image Format File*.txt text/plain Plain Text*.wdb application/vnd.ms-works MS Works Database*.wps application/vnd.ms-works Works Text Document*.xhtml application/xhtml+xml Extensible HyperText Markup Language*.xlc application/vnd.ms-excel MS Excel Chart*.xlm application/vnd.ms-excel MS Excel Macro*.xls application/vnd.ms-excel MS Excel Spreadsheet*.xlt application/vnd.ms-excel MS Excel Template*.xlw application/vnd.ms-excel MS Excel Workspace*.xml text/xml， application/xml Extensible Markup Language*.zip aplication/zip Compressed Archive