Backport _cleanups to Python 2 (#326)

backport of #325 to Python 2

Author: ilevkivskyi

python2/typing.py

@@ -665,9 +665,13 @@ def _check_generic(cls, parameters):
                         ("many" if alen > elen else "few", repr(cls), alen, elen))
 
 
+_cleanups = []
+
+
 def _tp_cache(func):
     maxsize = 128
     cache = {}
+    _cleanups.append(cache.clear)
 
     @functools.wraps(func)
     def inner(*args):