解决libxml/tree.h not found问题
1.targets->Build Phases->Link Binary With Libraries点击加号
2.输入libxml，添加libxml.dylib
3.点击Show in Finder
4，右键点击显示简介，找到SDK_DIR绝对路径
5，在终端输入命令：sudo ln -s /Volumes/Apple\ Xcode\ 4.6/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS6.1.sdk/usr/include/libxml2/libxml /usr/include/libxml
6，修改Header Search Pahts
