Change locking policy for Transaction

[someone1]

This was driving me up a wall, but nds treats transactions differently than the datastore package.

Specifically, it keeps an internal lock which is never unlocked after a commit or rollback. This will keep executing code deadlocked and is different than how the datastore package handles things.

Comments around this specify:

// tx.Unlock() is not called as the tx context should never be called
// again so we rather block than allow people to misuse the context.

Should we reconsider this policy or better document the difference in behavior from the datastore package?

[jongillham]

Are you talking about v2? If so are you allowed to try committing a transaction again if it fails?
Being able to match the datastore would be ideal.