Oooof ... fix this finally (save it into a variable that doesn't get unset). Close #294.

Author: ionelmc

src/pytest_cov/embed.py

@@ -97,8 +97,9 @@ def cleanup():
     _active_cov = None
     _cleanup_in_progress = False
     if _pending_signal:
+        pending_singal = _pending_signal
         _pending_signal = None
-        _signal_cleanup_handler(*_pending_signal)
+        _signal_cleanup_handler(*pending_singal)
 
 
 multiprocessing_finish = cleanup  # in case someone dared to use this internal