Make SIGINT handler kill the process tree

The std lib's `pdb` internals override SIGINT handling whenever one
enters the debugger repl. Force a handler that kills the tree if SIGINT
is triggered from the root actor, otherwise igore it since supervised
children should be managed already. This resolves an issue with guest
mode where `pdb` causes SIGINTs to be swallowed resulting in the host
loop never terminating the process tree.

tractor/_debug.py

@@ -11,7 +11,6 @@ from typing import Awaitable, Tuple, Optional, Callable, AsyncIterator
 from async_generator import aclosing
 import tractor
 import trio
-from trio.testing import wait_all_tasks_blocked
 
 from .log import get_logger
 from . import _state
@@ -132,9 +131,16 @@ async def _acquire_debug_lock(uid: Tuple[str, str]) -> AsyncIterator[None]:
         log.error(f"TTY lock released by {task_name}:{uid}")
 
 
-def handler(signum, frame):
-    """Block SIGINT while in debug to avoid deadlocks with cancellation.
+def handler(signum, frame, *args):
+    """Specialized debugger compatible SIGINT handler.
+
+    In childred we always ignore to avoid deadlocks since cancellation
+    should always be managed by the parent supervising actor. The root
+    is always cancelled on ctrl-c.
     """
+    if is_root_process():
+        tractor.current_actor().cancel_soon()
+    else:
         print(
             "tractor ignores SIGINT while in debug mode\n"
             "If you have a special need for it please open an issue.\n"
@@ -261,6 +267,7 @@ def _breakpoint(debug_func) -> Awaitable[None]:
             # may have the tty locked prior
             if _debug_lock.locked():  # root process already has it; ignore
                 return
+
             await _debug_lock.acquire()
             _pdb_release_hook = _debug_lock.release
 
@@ -269,7 +276,6 @@ def _breakpoint(debug_func) -> Awaitable[None]:
         log.debug("Entering the synchronous world of pdb")
         debug_func(actor)
 
-
     # user code **must** await this!
     return _bp()