ssh: fix flakey ssh errors on BSD systems

This is a trivial backport of c037fd655b47 performed by
[e-mail], but the change is still really Durham's not mine, so
I [augie] am leaving him as the author.

mercurial/sshpeer.py

@@ -190,12 +190,21 b' class sshpeer(wireproto.wirepeer):'
         self.pipei = doublepipe(self.ui, self.pipei, self.pipee)
         self.pipeo = doublepipe(self.ui, self.pipeo, self.pipee)
 
+        def badresponse():
+            self._abort(error.RepoError(_('no suitable response from '
+                                          'remote hg')))
+
+        try:
         # skip any noise generated by remote shell
         self._callstream("hello")
         r = self._callstream("between", pairs=("%s-%s" % ("0"*40, "0"*40)))
+        except IOError:
+            badresponse()
+
         lines = ["", "dummy"]
         max_noise = 500
         while lines[-1] and max_noise:
+            try:
             l = r.readline()
             self.readerr()
             if lines[-1] == "1\n" and l == "\n":
@@ -204,9 +213,10 b' class sshpeer(wireproto.wirepeer):'
                 self.ui.debug("remote: ", l)
             lines.append(l)
             max_noise -= 1
+            except IOError:
+                badresponse()
         else:
-            self._abort(error.RepoError(_('no suitable response from '
-                                          'remote hg')))
+            badresponse()
 
         self._caps = set()
         for l in reversed(lines):