Use python 2.6-compatible ascii encoding params
Merge branch 'develop' into feature/ElementTreeAdapter
ElementTree adapter code cleanup
Avoid creating adapter class instances when not necessary.

This change should improve performance, but most important will make it
possible to do  per-document caching of information in adapter instances.
Make it possible to manually clear cached data in adapters

This is only useful/necessary for the ElementTree adapter so far.
Cache ancestry lookup data in ElementTree adapter for performance