Makefile : add http_proxy in white list

Hello,
two things here :

* with the new whitelist trick, I could not download packages anymore through proxy, because wget needs to access the environment variable http_proxy. Two solutions : 
- instead of setting http_proxy in ~/.bashrc, set it in ~/.wgetrc (but it sucks because http_proxy was supposed to be used, and it is also used by other tools).
- use the following patch
It is more a proposal than a "request", you are the expert!

* add "or package not found" after package checksum check. I got mislead several times with this, thinking I could not download the package because of some checksum problem, while actually it was more a download problem.