pyparsing is needed by a couple different dependencies, including

setuptools, but versions newer than 2.4.x only support Python 3.
This change caps us at 2.4.x, in order to avoid any breakages during

installation.
We should now have every potentially-unsafe dependency included in a

default install of Review Board capped to a safe range. That should help

keep Review Board 3.0.x installable long-term, provided compatible

versions of Python and pip/easy_install.

Installed the package in a fresh virtualenv. Verified that it installed

without issues and that functionality seemed to work without errors.
Went through site-packages and checked each package, ensuring that any

that are a direct or indirect dependency of Review Board was capped,

explicitly a 2.7 backport of a Python 3 feature, or advertises long-term

support for Python 2.7.