Fix missing argument types in py3 stdlib (#995)

Still missing a few in _subprocess (a Windows-only private module) and decimal
(I gave up).

stdlib/3/_posixsubprocess.pyi

@@ -2,12 +2,13 @@
 
 # NOTE: These are incomplete!
 
-from typing import Tuple, Sequence
+from typing import Tuple, Sequence, Callable
 
 def cloexec_pipe() -> Tuple[int, int]: ...
 def fork_exec(args: Sequence[str],
-              executable_list, close_fds, fds_to_keep, cwd: str, env_list,
+              executable_list: Sequence[bytes], close_fds: bool, fds_to_keep: Sequence[int],
+              cwd: str, env_list: Sequence[bytes],
               p2cread: int, p2cwrite: int, c2pred: int, c2pwrite: int,
               errread: int, errwrite: int, errpipe_read: int,
-              errpipe_write: int, restore_signals, start_new_session,
-              preexec_fn) -> int: ...
+              errpipe_write: int, restore_signals: int, start_new_session: int,
+              preexec_fn: Callable[[], None]) -> int: ...

stdlib/3/http/client.pyi

@@ -7,6 +7,7 @@ from typing import (
 )
 import email.message
 import io
+from socket import socket
 import sys
 import ssl
 import types
@@ -87,7 +88,7 @@ if sys.version_info >= (3, 5):
         closed = ...  # type: bool
         status = ...  # type: int
         reason = ...  # type: str
-        def __init__(self, sock, debuglevel: int = ...,
+        def __init__(self, sock: socket, debuglevel: int = ...,
                      method: Optional[str] = ..., url: Optional[str] = ...) -> None: ...
         def read(self, amt: Optional[int] = ...) -> bytes: ...
         def readinto(self, b: bytearray) -> int: ...

stdlib/3/shlex.pyi

@@ -2,7 +2,7 @@
 
 # Based on http://docs.python.org/3.2/library/shlex.html
 
-from typing import List, Tuple, Any, TextIO
+from typing import List, Tuple, Any, TextIO, Union, Optional
 
 def split(s: str, comments: bool = ...,
           posix: bool = ...) -> List[str]: ...
@@ -26,7 +26,7 @@ class shlex:
     token = ...  # type: str
     eof = ...  # type: str
 
-    def __init__(self, instream=..., infile=...,
+    def __init__(self, instream: Union[str, TextIO] = ..., infile: Optional[str] = ...,
                  posix: bool = ...) -> None: ...
     def get_token(self) -> str: ...
     def push_token(self, tok: str) -> None: ...