nodelet demux assertion `px != 0' in onInit

[lucasw]

I'm using kinetic with Ubuntu 16.04 and compiling the nodelet demux header with -std=c++11 in https://github.com/lucasw/nodelet_demo (lucasw/nodelet_demo#1)

(The pcl demux also errors out on load, but maybe for different reasons?)

The crash happens at:

*pubs_output_[d] = private_nh_.template advertise<T> ((std::string)(output_topics_[d]), 1);

and the fix is:

pubs_output_[d] = boost::make_shared<ros::Publisher>(private_nh_.template advertise<T> ((std::string)(output_topics_[d]), 1));

I can provide a PR.