pkg_resources.require() in Python 3 raises TypeError instead of pkg_resources.DistributionNotFound

Originally reported by: arfrever (Bitbucket: arfrever, GitHub: arfrever)

$ python2.7 -c 'import pkg_resources; pkg_resources.require("aaa")'
-c:1: UserWarning: Unbuilt egg for setuptools [unknown version] (/tmp/setuptools)
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "pkg_resources.py", line 728, in require
    needed = self.resolve(parse_requirements(requirements))
  File "pkg_resources.py", line 622, in resolve
    raise DistributionNotFound(req)
pkg_resources.DistributionNotFound: aaa
$ python3.4 -c 'import pkg_resources; pkg_resources.require("aaa")'
-c:1: UserWarning: Unbuilt egg for setuptools [unknown version] (/tmp/setuptools)
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/tmp/setuptools/pkg_resources.py", line 728, in require
    needed = self.resolve(parse_requirements(requirements))
  File "/tmp/setuptools/pkg_resources.py", line 607, in resolve
    env = Environment(self.entries)
  File "/tmp/setuptools/pkg_resources.py", line 785, in __init__
    self.scan(search_path)
  File "/tmp/setuptools/pkg_resources.py", line 815, in scan
    self.add(dist)
  File "/tmp/setuptools/pkg_resources.py", line 835, in add
    dists.sort(key=operator.attrgetter('hashcmp'), reverse=True)
TypeError: unorderable types: NoneType() < str()

• Bitbucket: https://bitbucket.org/pypa/setuptools/issue/264

Reproduce the Python 2.7 and 3.4 commands from the issue, then inspect pkg_resources.py at require(), resolve(), Environment.scan(), and add(), where the Python 3 traceback reaches sorting. Done means requesting the missing aaa package on Python 3 raises pkg_resources.DistributionNotFound instead of TypeError.