Stop the futile process of trying to enumerate which kinds of exceptions distutils may throw (the latest potential addition: ValueError). Closes #1115.
This variable can be set to 0 to suppress or 1 to require the use of the extension (instead of the default to use it when it is available but silently fall back). Require the extension to be present on travis-ci.
This avoids the complexity of ensuring that cython is installed at build time.
This function has changed recently and it makes more sense to stop maintaining a separate copy, even though it does introduce our first required dependency.
This optimization is currently activated only if Cython is present when Tornado is installed.