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

Some of these are derived from mypy/stubs/.

2.7/signal.pyi

@@ -1,15 +1,11 @@
-"""Stub file for the 'signal' 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.
+from typing import Callable, Any, Tuple, Union
 
-from typing import Any, List, Tuple, Dict, GenericType
-
-ITIMER_PROF = ...  # type: long
+SIG_DFL = ...  # type: long
+SIG_IGN = ...  # type: long
 ITIMER_REAL = ...  # type: long
 ITIMER_VIRTUAL = ...  # type: long
-ItimerError = ...  # type: object
-NSIG = ...  # type: int
+ITIMER_PROF = ...  # type: long
+
 SIGABRT = ...  # type: int
 SIGALRM = ...  # type: int
 SIGBUS = ...  # type: int
@@ -45,31 +41,26 @@ SIGVTALRM = ...  # type: int
 SIGWINCH = ...  # type: int
 SIGXCPU = ...  # type: int
 SIGXFSZ = ...  # type: int
-SIG_DFL = ...  # type: long
-SIG_IGN = ...  # type: long
+NSIG = ...  # type: int
 
-def alarm(a: int) -> int: ...
+# Python 3 only:
+CTRL_C_EVENT = 0
+CTRL_BREAK_EVENT = 0
+GSIG = 0
 
+class ItimerError(IOError): ...
+
+_HANDLER = Union[Callable[[int, Any], Any], int, None]
+
+def alarm(time: int) -> int: ...
+def getsignal(signalnum: int) -> _HANDLER: ...
+def pause() -> None: ...
+def setitimer(which: int, seconds: float, interval: float = None) -> Tuple[float, float]: ...
+def getitimer(which: int) -> Tuple[float, float]: ...
+def set_wakeup_fd(fd: int) -> long: ...
+def siginterrupt(signalnum: int, flag: bool) -> None:
+    raise RuntimeError()
+def signal(signalnum: int, handler: _HANDLER) -> None:
+    raise RuntimeError()
 def default_int_handler(*args, **kwargs) -> Any:
     raise KeyboardInterrupt()
-
-def getitimer(a: int) -> tuple: ...
-
-def getsignal(a: int) -> None:
-    raise ValueError()
-
-def pause() -> None: ...
-
-def set_wakeup_fd(a: int) -> long:
-    raise ValueError()
-
-def setitimer(a: int, b: float, *args, **kwargs) -> tuple: ...
-
-def siginterrupt(a: int, b: int) -> None:
-    raise RuntimeError()
-    raise ValueError()
-
-def signal(a: int, b) -> None:
-    raise RuntimeError()
-    raise TypeError()
-    raise ValueError()