pager: check if signal.SIGPIPE exists

We have to check for signal.SIGPIPE before we attempt
to set it.

hgext/pager.py

@@ -85,10 +85,8 b' def uisetup(ui):'
                  (cmd not in ui.configlist('pager', 'ignore') and not attend))):
                 ui.setconfig('ui', 'formatted', ui.formatted())
                 ui.setconfig('ui', 'interactive', False)
-                try:
+                if util.safehasattr(signal, "SIGPIPE"):
                     signal.signal(signal.SIGPIPE, signal.SIG_DFL)
-                except ValueError:
-                    pass
                 _runpager(p)
         return orig(ui, options, cmd, cmdfunc)