(no ticket) Specify Django<1.6 in setup.py

This is quite urgent. Django 1.6 was released yesterday; without this
any new installation will be broken.

Already got a report: https://github.com/sio2project/oioioi/issues/10

Change-Id: I609cf427c78f776556533dade667f820093c83bf
Merge "(no ticket) Specify Django<1.6 in setup.py"