TwistedChecker fails on Python 2.6

[HawkOwl]

As reported by magmatt

$ twistedchecker twisted
Traceback (most recent call last):
  File "/Volumes/FatMan/home/matt/venvs/tmp/bin/twistedchecker", line 8, in <module>
    from twistedchecker.core.runner import Runner
  File "/Volumes/FatMan/home/matt/venvs/tmp/lib/python2.6/site-packages/twistedchecker/core/runner.py", line 59
    if disabledMessages != {""}:
                              ^
SyntaxError: invalid syntax

[HawkOwl (hawkowl)]

Okay, yeah, this is too much work. Py2.7 only, I think, and Py3 when it happens.