Extended gen_test decorator to pass args and kwargs.
A use case might be a decorated test class that passes arguments to each class method, like mock.patch for instance.
Merge pull request #1061 from stj/master

Extended gen_test decorator to pass args and kwargs.
Document gen_test change.
Point all links to the 'demos' directory to the stable branch instead of master.
Fix Tornado on Google App Engine.

Imports of tornado.ioloop have crept into more places, so the old
app engine policy of never importing these modules doesn't work.
Instead, we add guards around imports of unavailable modules
(fcntl, ssl, multiprocessing) so that everything is at least importable.

Closes #1059.