* cmp to reference db if --reference_chaindata provided
* graceful shutdown
* add ./cmd/integration to makefile
* add interruption support for different stages
* don't compare errors directly
* introduce PlainStateReader with fallbacks
* no 10.000 changes in tests
* even less iterations
* remove even more iterations
* add `go run ./cmd/geth --syncmode staged --plainstate` flag
* fix serialization calls
* make a more sensible file default
doesn’t affect anything, because this flag is always overriden when parsing CLI. but still.