Allow add_handlers() to append to existing hosts.

This change removes the restriction that all handlers for a given host
pattern be registered in a single call to add_handlers().
Merge branch 'master' into append-handlers
_get_host_handlers() now returns all host matches.

This approach has more clearly defined precedence rules than the
previous insertion-time strategy implemented in add_handlers().

It also correctly leaves pattern matching in the hands of the regular
expression evaluator as opposed to directly comparing pattern strings.
Avoid setting IOStream.error to wrong exception, close #651
Fix typo in releases/next.rst
Merge pull request #654 from davidwilemski/patch-1

Fix typo in releases/next.rst
Merge remote-tracking branch 'jparise/append-handlers' into merge
Release notes for add_headers change
Merge remote-tracking branch 'ajdavis/issue-651'
Allow tuples for the IOStream.close exc_info argument.

Update release notes.
Test with twisted 12.3
Fix an import that's been missing since the options/log refactoring.

Add a test for this previously-uncovered code.
Fix typo in docs
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.