When setup.py (with setuptools 12.0.5) is used with a pre-existing requests 0.8.2 (default on Ubuntu precise), it fails when checking whether the extra 'security' has been met.
```
Traceback (most recent call last):
File "setup.py", line 189, in <module>
use_2to3=False
File "/usr/lib/python2.7/distutils/core.py", line 152, in setup
dist.run_commands()
File "/usr/lib/python2.7/distutils/dist.py", line 953, in run_commands
self.run_command(cmd)
File "/usr/lib/python2.7/distutils/dist.py", line 972, in run_command
cmd_obj.run()
File "/home/travis/virtualenv/python2.7_with_system_site_packages/local/lib/python2.7/site-packages/nose/commands.py", line 144, in run
self.distribution.install_requires)
File "/home/travis/virtualenv/python2.7_with_system_site_packages/local/lib/python2.7/site-packages/setuptools/dist.py", line 311, in fetch_build_eggs
replace_conflicting=True,
File "/home/travis/virtualenv/python2.7_with_system_site_packages/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 813, in resolve
new_requirements = dist.requires(req.extras)[::-1]
File "/home/travis/virtualenv/python2.7_with_system_site_packages/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 2558, in requires
"%s has no such extra feature %r" % (self, ext)
pkg_resources.UnknownExtra: requests 0.8.2 has no such extra feature 'security'
```