add some missing constants (#1198)

Closes #2

stdlib/2and3/cgi.pyi

@@ -38,6 +38,7 @@ class MiniFieldStorage:
 
 
 class FieldStorage(object):
+    FieldStorageClass = ...  # type: Optional[type]
     keep_blank_values = ...  # type: int
     strict_parsing = ...  # type: int
     qs_on_post = ...  # type: Optional[str]

stdlib/2and3/copy.pyi

@@ -4,6 +4,9 @@ from typing import TypeVar, Optional, Dict, Any
 
 _T = TypeVar('_T')
 
+# None in CPython but non-None in Jython
+PyStringMap: Any
+
 # Note: memo and _nil are internal kwargs.
 def deepcopy(x: _T, memo: Optional[Dict[int, _T]] = ..., _nil: Any = ...) -> _T: ...
 def copy(x: _T) -> _T: ...

stdlib/2and3/hmac.pyi

@@ -9,6 +9,8 @@ _B = Union[bytes, bytearray]
 # TODO more precise type for object of hashlib
 _Hash = Any
 
+digest_size: None
+
 if sys.version_info >= (3, 4):
     def new(key: _B, msg: Optional[_B] = ...,
             digestmod: Optional[Union[str, Callable[[], _Hash], ModuleType]] = ...) -> HMAC: ...