Issue #20766: Merge with 3.5.

diff --cc Lib/pdb.py
index 7eb78b922ae731e548e005bbab6fc253bcf2c43d,47972655f969fc5aa9aea496e73d99c671cc02e2..97618b0ff16ab58287f5d2e21358b8c21da2ecac
--- 1/Lib/pdb.py
--- 2/Lib/pdb.py
+++ b/Lib/pdb.py
@@@ -135,8 -134,10 +135,10 @@@ line_prefix = '\n-> '   # Probably a be
  
  class Pdb(bdb.Bdb, cmd.Cmd):
  
+     _previous_sigint_handler = None
+ 
      def __init__(self, completekey='tab', stdin=None, stdout=None, skip=None,
 -                 nosigint=False):
 +                 nosigint=False, readrc=True):
          bdb.Bdb.__init__(self, skip=skip)
          cmd.Cmd.__init__(self, completekey, stdin, stdout)
          if stdout:

diff --cc Lib/test/test_pdb.py
Simple merge

diff --cc Misc/NEWS
index b9589e787a092625a55b8863a3ad730686338ada,28a7d944efbda9bda5859112cd5035d39a5b5d0b..667bff5eff09b7bebccef67d24bacec5201c5301
--- 1/Misc/NEWS
--- 2/Misc/NEWS
+++ b/Misc/NEWS
@@@ -2,29 -2,10 +2,32 @@@
  Python News
  +++++++++++
  
 -What's New in Python 3.5.3 release candidate 1?
 -===============================================
 +What's New in Python 3.6.0 beta 3
 +=================================
 +
 +*Release date: XXXX-XX-XX*
 +
 +Core and Builtins
 +-----------------
 +
 +Library
 +-------
 +
++- Issue #20766: Fix references leaked by pdb in the handling of SIGINT
++  handlers.
++
 +Build
 +-----
 +
 +- Issue #28208: Update Windows build to use SQLite 3.14.2.0.
  
 -Release date: TBA
 +- Issue #28248: Update Windows build to use OpenSSL 1.0.2j.
 +
 +
 +What's New in Python 3.6.0 beta 2
 +=================================
 +
 +*Release date: 2016-10-10*
  
  Core and Builtins
  -----------------