cleaner tqdm_notebook exit when not run in a notebook

[to266]

When not run in a notebook, the sp is not set. This checks if it is set, and exits cleanly.

The idea is to be able to do something like this (with appropriate catching if interested..):

from tqdm import tqdm, tqdm_notebook

def progressbar(*args, **kwargs):
    try:
        return tqdm_notebook(*args, **kwargs)
    except:
        return tqdm(*args, **kwargs)

This is a temporary workaround I found useful while waiting for #234

[coveralls]

Coverage remained the same at 90.776% when pulling 8073e69 on to266:notebook_try into 1167fed on tqdm:master.

[CrazyPython]

@lrq3000 reset the build, travis made an api error again

[lrq3000]

Damn coveralls, it should be disabled by now #263.

[codecov-io]

Current coverage is 90.56% (diff: 100%)

Merging #267 into master will not change coverage

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Powered by Codecov. Last update 1167fed...8073e69

[CrazyPython]

@lrq3000 not spamming anymore though...

Damn coveralls, it should be disabled by now #263.

This is what I love about open source and software development in general. Our non-for-profits are lean and snarky startups. And being able to say this too.

[lrq3000]

Thank you @to266 for the clean PR, merging it right now.