Switch from using html.fromstring to etree.fromstring

Also avoid doing explict encoding on byte-string provided by Django. XML
contains encoding information so lxml will do the right thing TM.
Test script for running non-integration tests.
Fix tests which send XML body
Added special character to successful payment XML to test encoding changes made in commit 6549864697fa3ff8231e2d7ffc8f424d7b252ed6
Added requirements back into this repo
Added lxml as a requirement

But note that normally it will be provided as a system package.
Force the testing tools to be locally installed

This worksaround the problem that drj has where nosetests is
already installed as a "site package".
Ignore venv
Merge pull request #3 from scraperwiki/encoding-error

Switch from using html.fromstring to etree.fromstring