support 'from __future__ import generators'

Cython/Compiler/Future.py

@@ -3,7 +3,7 @@ def _get_feature(name):
     try:
         return getattr(__future__, name)
     except AttributeError:
-        # unique fake object for earlier Python versions
+        # unique fake object for earlier Python versions or Python 3
         return object()
 
 unicode_literals = _get_feature("unicode_literals")
@@ -11,5 +11,6 @@ with_statement = _get_feature("with_statement")
 division = _get_feature("division")
 print_function = _get_feature("print_function")
 nested_scopes = _get_feature("nested_scopes")  # dummy
+generators = _get_feature("generators")  # dummy
 
 del _get_feature