[PATCH 5 of 5 STABLE] crecord: avoid setting non-existing SIGTSTP signal on windows (issue5512)

[Pierre-Yves David]

# HG changeset patch
# User Pierre-Yves David <pierre-yves.david at ens-lyon.org>
# Date 1491470905 -7200
#      Thu Apr 06 11:28:25 2017 +0200
# Branch stable
# Node ID cd0b74f1858c5e71a6f94c5ec195c070df6272a2
# Parent  f83025d451fa293849f819cc997bc3f8c9ce42e0
# EXP-Topic crecord-windows
# Available At https://www.mercurial-scm.org/repo/users/marmoute/mercurial/
#              hg pull https://www.mercurial-scm.org/repo/users/marmoute/mercurial/ -r cd0b74f1858c
crecord: avoid setting non-existing  SIGTSTP signal on windows (issue5512)

Windows do not have a SIGTSTP so we avoid setting the handler if the signal is
unknown.

diff --git a/mercurial/crecord.py b/mercurial/crecord.py
--- a/mercurial/crecord.py
+++ b/mercurial/crecord.py
@@ -473,14 +473,17 @@ def chunkselector(ui, headerlist, operat
     """
     ui.write(_('starting interactive selection\n'))
     chunkselector = curseschunkselector(headerlist, ui, operation)
-    f = signal.getsignal(signal.SIGTSTP)
+    origsigtstp = sentinel = object()
+    if util.safehasattr(signal, 'SIGTSTP'):
+        origsigtstp = signal.getsignal(signal.SIGTSTP)
     try:
         curses.wrapper(chunkselector.main)
         if chunkselector.initerr is not None:
             raise error.Abort(chunkselector.initerr)
         # ncurses does not restore signal handler for SIGTSTP
     finally:
-        signal.signal(signal.SIGTSTP, f)
+        if origsigtstp is not sentinel:
+            signal.signal(signal.SIGTSTP, origsigtstp)
     return chunkselector.opts
 
 def testdecorator(testfn, f):