Hye-Shik Chang's fix for Bug 875692.

Improve signal handling, especially when using threads, by forcing an early
re-execution of PyEval_EvalFrame() "periodic" code when things_to_do is not
cleared by Py_MakePendingCalls().

M Misc/NEWS
M Python/ceval.c
diff --git a/Python/ceval.c b/Python/ceval.c
index 4d26a7a..85e3518 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -786,6 +786,12 @@
 					why = WHY_EXCEPTION;
 					goto on_error;
 				}
+				if (things_to_do)
+					/* MakePendingCalls() didn't succeed.
+					   Force early re-execution of this
+					   "periodic" code, possibly after
+					   a thread switch */
+					_Py_Ticker = 0;
 			}
 #ifdef WITH_THREAD
 			if (interpreter_lock) {