This allows Travis to use the Docker container infrastructure, which should
make builds start up faster. See
http://docs.travis-ci.com/user/workers/container-based-infrastructure/

Add declared globals to each scope in the scope stack to avoid
erroneous UndefinedName errors when they are loaded.

Depending on the C library, some constants (like signal.SIGINT) might
not be defined. The previous code attempted to avoid failures on invalid
signals by catching the ValueError raised by signal.signal when given an
invalid signal to handle, however failed to account for the possiblity
of the signal not being defined at all.

Point people to GitHub, not Launchpad. All that's left on Launchpad are
a bunch of stale bugs.

Update the author field to reflect the large number of contributors.
Remove the maintainer field because a bug in something (setuptools?)
overwrites the author field with the maintainer field when the package
gets uploaded to PyPI.

Properly support list comprehensions in Python 3

List comprehensions have their own scope in Python 3.

https://docs.python.org/3/reference/expressions.html#displays-for-lists-sets-and-dictionaries

Remove unused class

[#885140] Update del handling in if and while statements.