Generalize beyond DPO, change condition for reset ReprP clock

[kris-brown]

This PR contains some general cleaning up, but most significantly:

• The code is now general for any rewriting semantics, not just DPO
• We update a representable clock if the number of parts has changed, rather than requiring that the update partial map be an isomorphism (which is a finer-grained condition: they come apart when you delete something and then add it back).
• Some [compat] entries have been added