all: integrate the freezer with fast sync

* all: freezer style syncing

core, eth, les, light: clean up freezer relative APIs

core, eth, les, trie, ethdb, light: clean a bit

core, eth, les, light: add unit tests

core, light: rewrite setHead function

core, eth: fix downloader unit tests

core: add receipt chain insertion test

core: use constant instead of hardcoding table name

core: fix rollback

core: fix setHead

core/rawdb: remove canonical block first and then iterate side chain

core/rawdb, ethdb: add hasAncient interface

eth/downloader: calculate ancient limit via cht first

core, eth, ethdb: lots of fixes

* eth/downloader: print ancient disable log only for fast sync

les/odr_requests.go

@@ -514,7 +514,7 @@ func (r *TxStatusRequest) Validate(db ethdb.Database, msg *Msg) error {
 // readTraceDB stores the keys of database reads. We use this to check that received node
 // sets contain only the trie nodes necessary to make proofs pass.
 type readTraceDB struct {
-	db    ethdb.Reader
+	db    ethdb.KeyValueReader
 	reads map[string]struct{}
 }