dirstate-scoping [10] : start warning/breaking on bad usage

After a very long journey, we can finally start reaping some benefit.

Depends on:

• !424 (merged)
• !425 (merged)
• !426 (merged)
• !427 (merged)
• !429 (merged)
• !430 (merged)
• !415 (merged)
• !432 (merged)
• !433 (merged)