Fix for issue #307

dist was skipping over pipes when one failed because the non-working pipe got
swapped with a working pipe but the write was never retried on that pipe

src/dist.cpp

@@ -139,7 +139,8 @@ void zmq::dist_t::distribute (msg_t *msg_, int flags_)
 
     if (msg_->is_vsm ()) {
         for (pipes_t::size_type i = 0; i < matching; ++i)
-            write (pipes [i], msg_);
+            if(!write (pipes [i], msg_))
+                --i; //  Retry last write because index will have been swapped
         int rc = msg_->close();
         errno_assert (rc == 0);
         rc = msg_->init ();
@@ -154,8 +155,10 @@ void zmq::dist_t::distribute (msg_t *msg_, int flags_)
     //  Push copy of the message to each matching pipe.
     int failed = 0;
     for (pipes_t::size_type i = 0; i < matching; ++i)
-        if (!write (pipes [i], msg_))
+        if (!write (pipes [i], msg_)) {
             ++failed;
+            --i; //  Retry last write because index will have been swapped
+        }
     if (unlikely (failed))
         msg_->rm_refs (failed);