build-i18n.py, which is a necessary part of the package build process,

was assuming it had the right version of Review Board and Django in the

import path when it began importing modules. While this is often going

to be the case when building packages, it's not necessarily the case in

CI.
Our build-media.py script has code to set up the correct environment

before doing imports, so it was able to work fine in CI. This change

simply copies over that logic to build-i18n.py.

Built the package successfully.