Fix msvc compile error and improve 64 bit compatibility
Merge pull request #973 from cgohlke/patch-1

Fix msvc compile error and improve 64 bit compatibility
Add a new TORNADO_EXTENSION environment variable for testing purposes.

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.
Add better debugging for ImportErrors resulting from TORNADO_EXTENSION=1
Reinstate the 'cd maint' in .travis.yml.

This turned out to be breaking the speedups module.
Don't require the extension to be present when building docs.
Merge branch 'branch3.2'
Require the extension to be built in tox -full runs.