Apply fixes, remove duplicates.

Apply fixes to _random, cStringIO, errno, operator, sys, zlib, etc.; also,
remove duplicate 2.7/math.pyi, 2.7/marshal.pyi.

builtins/2.7/cStringIO.pyi

@@ -1,10 +1,7 @@
 # Stubs for cStringIO (Python 2.7)
-# Built from https://docs.python.org/2/library/stringio.html
+# See https://docs.python.org/2/library/stringio.html
 
-from typing import IO, List, Iterable, Iterator, Any
-
-InputType = ... # type: type
-OutputType = ... # type: type
+from typing import IO, List, Iterable, Iterator, Any, Union
 
 class StringIO(IO[str]):
     softspace = ... # type: int
@@ -18,17 +15,24 @@ class StringIO(IO[str]):
     def flush(self) -> None: ...
     def isatty(self) -> bool: ...
     def read(self, size: int = -1) -> str: ...
-    def write(self, b: str) -> None: ...
     def readable(self) -> bool: ...
     def readline(self, size: int = -1) -> str: ...
     def readlines(self, hint: int = -1) -> List[str]: ...
     def seek(self, offset: int, whence: int = ...) -> None: ...
     def seekable(self) -> bool: ...
     def tell(self) -> int: ...
-    def truncate(self, size: int = None) -> int: ...
+    def truncate(self, size: int = None) -> int:
+        raise IOError()
     def writable(self) -> bool: ...
     def writelines(self, lines: Iterable[str]) -> None: ...
     def next(self) -> str: ...
-    def __iter__(self) -> Iterator[str]: ...
+    def __iter__(self) -> "InputType": ...
     def __enter__(self) -> Any: ...
     def __exit__(self, exc_type: type, exc_val: Any, exc_tb: Any) -> Any: ...
+    # only StringO:
+    def reset() -> None: ...
+    def write(self, b: Union[str, unicode]) -> None: ...
+    def writelines(self, lines: Iterable[Union[str, unicode]]) -> None: ...
+
+InputType = StringIO
+OutputType = StringIO