operator<< for std::unique_ptr

Not an option when logging stl structures containing `std::unique_ptr`s. Tested, and works. This is what `stl_logging.h` [url=https://code.google.com/p/google-glog/source/browse/trunk/src/windows/glog/stl_logging.h?r=105#42]does[/url] too btw (and it appears to work without this `using`), it's just that the version we have doesn't support `std::unique_ptr`. We may want to add this as a patch to glog (but it's not necessary), this is a valid temporary fix.
Reopening.