Please backport flask-babel 0.9-2.1 (universe) from xenial

[Frédéric Bonnard]

Please backport flask-babel 0.9-2.1 (universe) from xenial to trusty.

Reason for the backport:
========================
To be able to run https://github.com/NVIDIA/DIGITS on trusty, a few packages
are needed as dependencies for https://github.com/miguelgrinberg/Flask-SocketIO
which itself is needed by DIGITS.

Testing:
========
Mark off items in the checklist [X] as you test them, but please leave the checklist so that backporters can quickly evaluate the state of testing.

You can test-build the backport in your PPA with backportpackage:
$ backportpackage -u ppa:<lp username>/<ppa name> -s xenial -d trusty flask-babel

* trusty:
[X] Package builds without modification
[X] python-flask-babel-doc installs cleanly and runs
[X] python-flask-babel installs cleanly and runs
[X] python3-flask-babel installs cleanly and runs

No reverse dependencies