Refs #20461 -- Add tblib to py2 requirements.txt

[collinanderson]

https://code.djangoproject.com/ticket/20461#comment:21

[bak1an]

Please add to py3 requirements as well.

[bak1an]

It also would be helpful to add this to documentation as well, because current wording sounds like "you can install tblib to see pretty stacktraces, but you can skip it if you don't care". This should sound more like "tblib is totally required (at least to run tests in parallel)".

[timgraham]

This is already in the base.txt requirements file?

[bak1an]

Please add to py3 requirements as well.

or to base.txt

[collinanderson]

I think tblib more optional on python3, but I might be wrong. (Because tracebacks are pickable on py3?)

Hah. yup. It's already in base.txt. :)

[bak1an]

@collinanderson
It crashed withoud tblib on py3.4 for me.

But anyway, I should have missed the actual change within b1a2954 that adds tblib to base.txt while looking for the new requirements to install within diff.

Sorry for a mess :)