Issue #8407, issue #11859: Add signal.pthread_sigmask() function to fetch
and/or change the signal mask of the calling thread.

Fix also tests of test_io using threads and an alarm: use pthread_sigmask() to
ensure that the SIGALRM signal is received by the main thread.

Original patch written by Jean-Paul Calderone.
diff --git a/Misc/NEWS b/Misc/NEWS
index 37ac3e7..1230a68 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -127,6 +127,9 @@
 Library
 -------
 
+- Issue #8407: Add signal.pthread_sigmask() function to fetch and/or change the
+  signal mask of the calling thread.
+
 - Issue #11858: configparser.ExtendedInterpolation expected lower-case section
   names.
 
@@ -531,6 +534,10 @@
 Tests
 -----
 
+- Issue #8407, #11859: Fix tests of test_io using threads and an alarm: use
+  pthread_sigmask() to ensure that the SIGALRM signal is received by the main
+  thread.
+
 - Issue #11811: Factor out detection of IPv6 support on the current host
   and make it available as ``test.support.IPV6_ENABLED``.  Patch by
   Charles-François Natali.