Added support for python 3 and NCCL

[willyd]

@cypof I reworked the NCCL and python3 compatibility of #5400. Can you try this and let me know.

[cypof]

OK, everything seems to work, thanks

[willyd]

Thanks

[lvzhaoyang]

Hi,

I have compiling issue which is

/home/zlv30/framework/caffe/python/caffe/_caffe.cpp: In function ‘boost::python::api::object caffe::NCCL_New_Uid()’:
/home/zlv30/framework/caffe/python/caffe/_caffe.cpp:374:10: error: could not convert ‘uid’ from ‘std::__cxx11::string {aka std::__cxx11::basic_string<char>}’ to ‘boost::python::api::object’
   return uid;

which I think it is caused by this pull request. Can you take a look at it?

I am using python 2 on ubuntu 16.04.

[willyd]

This was supposed to be fixed in eeebdab

@lvzhaoyang Can you confirm that you are using the latest master?