Drop py25 from the main tox.ini
Add tornado.util.u and a fixer script to start using it.
Add a simple sanity-check test for locale data.
Convert all unicode literals to tornado.util.u.

Mostly done by the fixer script with manual import updates,
although the raw literal in escape.py needed special handling.
Change "except Type, value" to "except Type as value".

Necessary for py3, supported since py26.
2to3 -n -w -f except tornado
Convert print to a function and add future imports.

Automated with 2to3 and custom fixer.
2to3 -f print tornado > print.diff
2to3 -f print -d tornado > print_doctest.diff
maint/scripts/run_fixers.py -f future_import tornado > future.diff
cd tornado
git apply ../{print,print_doctest,future}.diff
Checkpoint: tests can now be imported in python 3 without 2to3.

The tests are not passing, but this fixes up all the import-time problems.
The tests still work under 2to3 or python 2.
Get autoreload working in py3 without 2to3.
Get all the tests passing under py3 without 2to3
Remove more py25 testing configs
Remove our custom epoll module now that we only support 2.6+.