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

core/rawdb/schema.go

@@ -63,6 +63,23 @@ var (
 	preimageHitCounter = metrics.NewRegisteredCounter("db/preimage/hits", nil)
 )
 
+const (
+	// freezerHeaderTable indicates the name of the freezer header table.
+	freezerHeaderTable = "headers"
+
+	// freezerHashTable indicates the name of the freezer canonical hash table.
+	freezerHashTable = "hashes"
+
+	// freezerBodiesTable indicates the name of the freezer block body table.
+	freezerBodiesTable = "bodies"
+
+	// freezerReceiptTable indicates the name of the freezer receipts table.
+	freezerReceiptTable = "receipts"
+
+	// freezerDifficultyTable indicates the name of the freezer total difficulty table.
+	freezerDifficultyTable = "diffs"
+)
+
 // LegacyTxLookupEntry is the legacy TxLookupEntry definition with some unnecessary
 // fields.
 type LegacyTxLookupEntry struct {