Update pytest requirement.

This breaks Travis.

    pkg_resources.VersionConflict: (pytest 2.6.3 (/home/travis/virtualenv/python2.7.8/lib/python2.7/site-packages), Requirement.parse('pytest==2.6.1'))
Remove unused install_requires parameter in setup.py.

Also, renamed PyTest class to PyTestCommand and made
a couple cosmetic changes.
Python 3.1 is not supported anymore.
Merge pull request #914 from berkerpeksag/remove-3.1-support

Python 3.1 is not supported anymore.
Merge pull request #913 from berkerpeksag/tweak-setup

Remove unused install_requires parameter in setup.py.
Simplify recursive-exclude rules in MANIFEST.in.
Merge pull request #916 from berkerpeksag/cleanup-manifest

Simplify recursive-exclude rules in MANIFEST.in.
Add selectors module to gunicorn codebase.

Closes #886.
remove option --debug and update documents
Merge pull request #918 from menghan/remove-deprecated

Remove deprecated option --debug, fix #917
Add a news entry for #917.
Use tox in .travis.yml.

This way we can avoid code duplication.

Also, this change makes tests faster due to ignoring the sdist step
and adds Python 3.2, 3.4 and PyPy 3 to build matrix.
Merge pull request #919 from berkerpeksag/cleanup-scripts

Use tox in .travis.yml.
uses gunicorn.selectors when python < 3.4
gthread: improve accepting connections loop

make sure we stop accepting immediately when max connections is achieved.
allows to enable/disable the use of sendfile()

fix #856
fix method call.
Add a versionadded directive to the sendfile documentation.
Merge branch 'master' into alq666/appname-statsd
Support prefix and statsd tags