Add ability to get/set HTTP response reason phrase in RequestHandler and HTTPResponse
Add concurrent.futures as an optional dependency for -full builds
Add IOLoop.add_future to return to the IOLoop after a future has completed.
Add futures-based Resolver interface, and test with both sync and thread pool.
Capture stack_context in IOLoop.add_future
Use new async resolver interface in simple_httpclient.
Improve autoreload for import-time errors.

We already had a special case for SyntaxErrors, but NameErrors and other
import-time errors could leave a file unwatched.
Flesh out future-oriented client interfaces.

Make DummyFuture a more complete imitation of Future.

Add tests demonstrating various implementation styles.

Add a decorator that simplifies use of futures.
Add gen.YieldFuture.
Add magic for yielding futures.

Introduce IOLoop.current() as a thread-local counterpart to IOLoop.instance().

gen.engine now recognizes Futures directly.
Merge branch 'master' into futures
Mention HTTPError explicitly in the write_error docs.

Closes #594.
Remove tornado.database, which is now distributed separately.
Split IOStream into BaseIOStream and IOStream.

IOStream the socket-specific code; BaseIOStream will be the basis
for non-socket-based streams (i.e. pipes)
Add PipeIOStream
Add tornado.process.Subprocess
Release notes.
Add a SIGCHILD handler to Subprocess.
Skip pipe and subprocess tests on windows.
Subprocess.returncode should match subprocess.Popen.returncode.