Fixed bootstrap script.

Made compatible with Python 2.6.
The bootstrap/makebootstrap.py will allways run.
Fixed relativ link targets im openid in GAE examples to absolute.
GAE download is skipped on Python 2.6.
Cleaned up requirements.
Added venv26 to .gitignore.
Fixed a bug when deserialized session key could not unpickled.
Made compatible with Python 2.6.