PYTHON-1541 - Use setuptools python_requires

To enforce minimum Python requirements.

Author: behackett

setup.py

@@ -366,6 +366,7 @@ def build_extension(self, ext):
  keywords=["mongo", "mongodb", "pymongo", "gridfs", "bson"],
  install_requires=[],
  license="Apache License, Version 2.0",
+ python_requires=">=2.7,!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*",
  classifiers=[
  "Development Status :: 5 - Production/Stable",
  "Intended Audience :: Developers",