bpo-30057: Fix potential missed signal in signal.signal(). (#4258)

Bug report and patch by Jeroen Demeyer.
diff --git a/Misc/ACKS b/Misc/ACKS
index 1bd3c04..0511390 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -362,6 +362,7 @@
 Arnaud Delobelle
 Konrad Delong
 Erik Demaine
+Jeroen Demeyer
 Martin Dengler
 John Dennis
 L. Peter Deutsch
diff --git a/Misc/NEWS.d/next/Library/2017-11-03-19-11-43.bpo-30057.NCaijI.rst b/Misc/NEWS.d/next/Library/2017-11-03-19-11-43.bpo-30057.NCaijI.rst
new file mode 100644
index 0000000..5740eb2
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2017-11-03-19-11-43.bpo-30057.NCaijI.rst
@@ -0,0 +1 @@
+Fix potential missed signal in signal.signal().