Make multiprocessing.Queue a subclass of queue.Queue (#1525)

Also change multiprocessing.Queue's put and get timeout arguments to
allow None.

This fixes a problem with logging.handlers.QueueHandler and
QueueListener not accepting a multiprocessing.Queue as the queue
argument.

Declaring the Queue now needs to note what it will be used for. eg.
q = multiprocessing.Queue()    # type: multiprocessing.Queue[List[Any]]

stdlib/3/multiprocessing/__init__.pyi

@@ -1,6 +1,6 @@
 # Stubs for multiprocessing
 
-from typing import Any, Callable, Iterable, Mapping, Optional, Dict, List, Union
+from typing import Any, Callable, Iterable, Mapping, Optional, Dict, List, Union, TypeVar
 
 from logging import Logger
 from multiprocessing.context import BaseContext
@@ -8,6 +8,9 @@ from multiprocessing.managers import SyncManager
 from multiprocessing.pool import AsyncResult
 from multiprocessing.process import current_process as current_process
 import sys
+import queue
+
+_T = TypeVar('_T')
 
 class Lock():
     def acquire(self, block: bool = ..., timeout: int = ...) -> None: ...
@@ -93,15 +96,15 @@ class Process():
     def is_alive(self) -> bool: ...
     def join(self, timeout: Optional[float] = ...) -> None: ...
 
-class Queue():
+class Queue(queue.Queue[_T]):
     def __init__(self, maxsize: int = ...) -> None: ...
-    def get(self, block: bool = ..., timeout: float = ...) -> Any: ...
-    def put(self, item: Any, block: bool = ..., timeout: float = ...) -> None: ...
+    def get(self, block: bool = ..., timeout: Optional[float] = ...) -> _T: ...
+    def put(self, item: _T, block: bool = ..., timeout: Optional[float] = ...) -> None: ...
     def qsize(self) -> int: ...
     def empty(self) -> bool: ...
     def full(self) -> bool: ...
-    def put_nowait(self, item: Any) -> None: ...
-    def get_nowait(self) -> Any: ...
+    def put_nowait(self, item: _T) -> None: ...
+    def get_nowait(self) -> _T: ...
     def close(self) -> None: ...
     def join_thread(self) -> None: ...
     def cancel_join_thread(self) -> None: ...