Better extras_requires handling.

Author: manuco

setup.py

@@ -41,8 +41,13 @@ def run(cls):
         "lz4": ["lz4"],
         "snappy": ["python-snappy"],
         "zstd": ["python-zstandard"],
-        # "gssapi": ["gssapi"],
-        # "gssapi_sspi": ["pywin32"],
+        "gssapi": ["gssapi"],
+        "sspi": ["pywin32 >= 301"],
+        "krb5_auto": [
+            'pywin32>=301;platform_system=="Windows"',
+            'gssapi;platform_system=="Linux"',
+        ],
+
     },
     cmdclass={"test": Tox},
     packages=find_packages(exclude=['test']),
@@ -58,8 +63,6 @@ def run(cls):
         "Intended Audience :: Developers",
         "License :: OSI Approved :: Apache Software License",
         "Programming Language :: Python",
-        "Programming Language :: Python :: 2",
-        "Programming Language :: Python :: 2.7",
         "Programming Language :: Python :: 3",
         "Programming Language :: Python :: 3.4",
         "Programming Language :: Python :: 3.5",