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/state/database.go

@@ -93,7 +93,7 @@ type Trie interface {
 	// If the trie does not contain a value for key, the returned proof contains all
 	// nodes of the longest existing prefix of the key (at least the root), ending
 	// with the node that proves the absence of the key.
-	Prove(key []byte, fromLevel uint, proofDb ethdb.Writer) error
+	Prove(key []byte, fromLevel uint, proofDb ethdb.KeyValueWriter) error
 }
 
 // NewDatabase creates a backing store for state. The returned database is safe for