pickle: sync Python 2.7 stubs with Python 3 version

The Python 3 version was added in 94467be.

stdlib/2.7/pickle.pyi

@@ -1,8 +1,38 @@
 # Stubs for pickle (Python 2)
 
-from typing import Any, IO
+from typing import Any, BinaryIO
 
-def dump(obj: Any, file: IO[str], protocol: int = ...) -> None: ...
-def dumps(obj: Any, protocol: int = ...) -> str: ...
-def load(file: IO[str]) -> Any: ...
-def loads(str: str) -> Any: ...
+
+HIGHEST_PROTOCOL = ...  # type: int
+
+
+def dump(obj: Any, file: BinaryIO, protocol: int = None) -> None: ...
+def dumps(obj: Any, protocol: int = ...) -> bytes: ...
+def load(file: BinaryIO) -> Any: ...
+def loads(string: bytes) -> Any: ...
+
+
+class PickleError(Exception):
+    pass
+
+
+class PicklingError(PickleError):
+    pass
+
+
+class UnpicklingError(PickleError):
+    pass
+
+
+class Pickler:
+    def __init__(self, file: BinaryIO, protocol: int = None) -> None: ...
+
+    def dump(self, obj: Any) -> None: ...
+
+    def clear_memo(self) -> None: ...
+
+
+class Unpickler:
+    def __init__(self, file: BinaryIO) -> None: ...
+
+    def load(self) -> Any: ...