Catch cancellation as part of BaseException (python/cpython#13528)

* See also: https://bugs.python.org/issue32528

* This change makes actxmgr cancellation behaviors in Python 3.6/3.7/3.8 consistent.

Author: achimnol

src/aiotools/context.py

@@ -135,7 +135,7 @@ async def __aexit__(self, exc_type, exc_value, tb):
                             return False
                     # If this is a purely new exception, raise the new one.
                     raise
-                except BaseException as exc:
+                except (BaseException, asyncio.CancelledError) as exc:
                     if exc is not exc_value:
                         raise
 

src/aiotools/server.py

@@ -120,7 +120,7 @@ async def __aexit__(self, exc_type, exc_value, tb):
                     if exc_new_value.__cause__ is exc_value:
                         return False
                 raise
-            except BaseException as exc:
+            except (BaseException, asyncio.CancelledError) as exc:
                 if exc is not exc_value:
                     raise