Copying error does not include newlines

[astrofrog]

When copying an error from the error console, the output is something like:

Traceback (most recent call last):
  File "/Users/tom/miniconda3/envs/gluedev/lib/python3.4/site-packages/glueviz-0.5.0-py3.4.egg/glue/core/application_base.py", line 25, in wrapper
    return func(*args, **kwargs)
  File "/Users/tom/miniconda3/envs/gluedev/lib/python3.4/site-packages/glueviz-0.5.0-py3.4.egg/glue/core/application_base.py", line 94, in save_session
    state = gs.dumps(indent=2)
  File "/Users/tom/miniconda3/envs/gluedev/lib/python3.4/site-packages/glueviz-0.5.0-py3.4.egg/glue/core/state.py", line 339, in dumps
    return json.dumps(result, indent=indent, default=self.json_default)
  File "/Users/tom/miniconda3/envs/gluedev/lib/python3.4/json/__init__.py", line 237, in dumps
    **kw).encode(obj)
  File "/Users/tom/miniconda3/envs/gluedev/lib/python3.4/json/encoder.py", line 194, in encode
    chunks = list(chunks)
  File "/Users/tom/miniconda3/envs/gluedev/lib/python3.4/json/encoder.py", line 422, in _iterencode
    yield from _iterencode_dict(o, _current_indent_level)
  File "/Users/tom/miniconda3/envs/gluedev/lib/python3.4/json/encoder.py", line 396, in _iterencode_dict
    yield from chunks
  File "/Users/tom/miniconda3/envs/gluedev/lib/python3.4/json/encoder.py", line 396, in _iterencode_dict
    yield from chunks
  File "/Users/tom/miniconda3/envs/gluedev/lib/python3.4/json/encoder.py", line 430, in _iterencode
    yield from _iterencode(o, _current_indent_level)
  File "/Users/tom/miniconda3/envs/gluedev/lib/python3.4/json/encoder.py", line 427, in _iterencode
    raise ValueError("Circular reference detected")
ValueError: Circular reference detected


Newlines are missing...

[astrofrog]

They are not missing but use the unicode \u2029. This PR normalizes this.