update PYTHONPATH in ipython launcher
update PYTHONPATH in ipython launcher

Summary:
I followed installation [instructions](https://github.com/caffe2/caffe2/blob/master/README.md#os-x) for OS-X. Works perfect. After installation instructions, ipython notebook works with the updated PYTHONPATH.
Closes https://github.com/caffe2/caffe2/pull/145

Reviewed By: bwasti

Differential Revision: D4551908

Pulled By: Yangqing

fbshipit-source-id: 591d750fd9ed3ede5f24d4837e9a6a7044ec49bf

sf-wind/caffe2,Yangqing/caffe2,bwasti/caffe2,davinwang/caffe2,pietern/caffe2,Yangqing/caffe2,sf-wind/caffe2,pietern/caffe2,bwasti/caffe2,davinwang/caffe2,sf-wind/caffe2,davinwang/caffe2,bwasti/caffe2,davinwang/caffe2,davinwang/caffe2,caffe2/caffe2,pietern/caffe2,Yangqing/caffe2,xzturn/caffe2,bwasti/caffe2,pietern/caffe2,bwasti/caffe2,pietern/caffe2,xzturn/caffe2,xzturn/caffe2,xzturn/caffe2,sf-wind/caffe2,Yangqing/caffe2,sf-wind/caffe2,xzturn/caffe2,Yangqing/caffe2