IPython redirect stdout

We used to set `Base.stdout` to `PyIO(sys.stdout)` but this causes bugs so is removed.

Instead copy the IJulia approach: use `pipe = redirect_stdout()` and have an async task watch the pipe for output and write it to `sys.stdout`.

Locate the code that sets Base.stdout to PyIO(sys.stdout), then inspect how redirect_stdout() and the IJulia approach handle the pipe. Trace how an async task could observe pipe output and forward it to sys.stdout. Done means IPython output is redirected without the bugs caused by the previous Base.stdout assignment.

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