Improve several stubs. (math, _random, time, etc.)

Some of these are derived from mypy/stubs/.

2.7/gc.pyi

@@ -1,33 +1,27 @@
-"""Stub file for the 'gc' module."""
-# This is an autogenerated file. It serves as a starting point
-# for a more precise manual annotation of this module.
-# Feel free to edit the source below, but remove this header when you do.
+# Stubs for gc (Python 2)
 
-from typing import Any, List, Tuple, Dict, GenericType
-
-def collect(*args, **kwargs) -> int:
-    raise ValueError()
-
-def disable() -> None: ...
+from typing import List, Any, Tuple
 
 def enable() -> None: ...
-
-def get_count() -> tuple: ...
-
-def get_debug() -> int: ...
-
-def get_objects() -> list: ...
-
-def get_referents(*args, **kwargs) -> list: ...
-
-def get_referrers(*args, **kwargs) -> list: ...
-
-def get_threshold() -> tuple: ...
-
-def is_tracked(*args, **kwargs) -> bool: ...
-
+def disable() -> None: ...
 def isenabled() -> bool: ...
+def collect(generation: int = None) -> int: ...
+def set_debug(flags: int) -> None: ...
+def get_debug() -> int: ...
+def get_objects() -> List[Any]: ...
+def set_threshold(threshold0: int, threshold1: int = None, threshold2: int = None) -> None: ...
+def get_count() -> Tuple[int, int, int]: ...
+def get_threshold() -> Tuple[int, int, int]: ...
+def get_referrers(*objs: Any) -> List[Any]: ...
+def get_referents(*objs: Any) -> List[Any]: ...
+def is_tracked(obj: Any) -> bool: ...
 
-def set_debug(a: int) -> None: ...
+garbage = ... # type: List[Any]
 
-def set_threshold(a: int, *args, **kwargs) -> None: ...
+DEBUG_STATS = ... # type: Any
+DEBUG_COLLECTABLE = ... # type: Any
+DEBUG_UNCOLLECTABLE = ... # type: Any
+DEBUG_INSTANCES = ... # type: Any
+DEBUG_OBJECTS = ... # type: Any
+DEBUG_SAVEALL = ... # type: Any
+DEBUG_LEAK = ... # type: Any