Create custom pickle serializer.

We need to do this because when I tride to go to the JSON serializer a
bunch of tests started failing because various parts of our code are
putting things into the session that are not JSON serializable.

We can't keep using the default pickle serializer because it defaluts to
using the highest available protocol and that will cause issues with the
python 2 to 3 upgrade since both will be running in production at the
same time.  We need to use a version of the pickle protocol that both
can use interchangably.

We also need to make sure we read with latin1 encoding to make datetimes
work correctly between the two versions of python.