Update wechatext.class.php

修复读取cookie失效
增加JS调用微信内图片预览组件支持。
Merge pull request #113 from htwyqjj/patch-1

Update wechatext.class.php
Merge branch 'master' of https://github.com/dodgepudding/wechat-php-sdk.git
merge update from @binsee
补全遗漏方法
Merge branch 'master' of git@github.com:dodgepudding/wechat-php-sdk.git

Conflicts:
	Thinkphp/Wechat.class.php
	Thinkphp/Wechatext.class.php
	wechat.class.php
	wechat.js