python 3.3 port (same sourcecode support 2.6/2.7/3.3)

Used the same method as in flask, importing compat stuff from
flask._compat.

Changed requirements to also fetch werkzeug from git as it otherwise
fetches a non-py33 compatible version.

All tests succeed for 2.x, there is still 1 strange failure left on 3.3
that seems somehow unrelated to the changes done for the port.