Ubuntu14.04在virtualenv下安装scrapy报错，Failed building wheel for cffi,lxml,cryptography 等. error: command 'x86_64-linux-gnu-gcc' failed with exit status 1
sudo apt-get build-dep python-lxml
sudo pip install lxml --upgrade
sudo apt-get install build-essential libssl-dev libffi-dev python-dev
pip install scrapy
参考链接：
http://www.cnblogs.com/ifantastic/p/3830707.html
http://stackoverflow.com/questions/22073516/failed-to-install-python-cryptography-package-with-pip-and-setup-py