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'