Fix exception in StaticFileHandler when range requested is larger than file.
RequestHandler sets its close callback on the HTTPConnection, not the IOStream.

Fixes a bug in which close callbacks would never be called for subsequent
requests on a reused connection.
Add 3.1.1 release notes.
Set version number to 3.1.1
Merge branch 'branch3.1'

Conflicts:
	docs/releases.rst
	setup.py
	tornado/__init__.py