Make IPython work if a recent numpy is not available. I updated the numpy testing decorators module and didn't notice they recently introduced dependencies that make it use the rest of numpy. We may later want to revisit this, as my solution is ugly, but I simply hacked it to load locally the code they added, which we now carry as _numpy_testing_utils. Ultimately the solution to this should be taken up with upstream numpy, so that we all agree on a common set of testing decorators with no other dependencies aside from the stdlib. But for now, this will let us move forward as that discussion could take a while.