Summary:
Pull Request resolved: pytorch/pytorch#10546

Have you ever written an operator<< overload in the caffe2 namespace
in a core Caffe2 header, and then been stunned when some completely
unrelated code started breaking?  This diff fixes this problem!

The problem looks like this:
1. You're building against a really old version of glog (think 0.3.2,
   or something like that)
2. This version of glog defines operator<< overloads for std containers
   in the global namespace
3. You add a new overload in your current namespace (e.g., caffe2).
   Congratulations: this overload is *preferentially* chosen over
   the global namespace one for all calls to << in that namespace.
   And since it doesn't actually have std::vector overloads, unrelated
   Caffe2 code breaks.

Newer versions of glog have a fix for this: they have the line:

  namespace std { using ::operator<<; }

in their header.  So let's help old versions of glog out and do this ourselves.

In our new world order, operator<< overloads defined in the global namespace
won't work (unless they're for std containers, which work because of ADL).
So this diff also moves all those overloads to the correct namespace.

Reviewed By: dzhulgakov

Differential Revision: D9344540

fbshipit-source-id: 6246ed50b86312668ebbd7b039fcd1233a3609cf