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

ethdb/batch.go

@@ -23,7 +23,7 @@ const IdealBatchSize = 100 * 1024
 // Batch is a write-only database that commits changes to its host database
 // when Write is called. A batch cannot be used concurrently.
 type Batch interface {
-	Writer
+	KeyValueWriter
 
 	// ValueSize retrieves the amount of data queued up for writing.
 	ValueSize() int
@@ -35,7 +35,7 @@ type Batch interface {
 	Reset()
 
 	// Replay replays the batch contents.
-	Replay(w Writer) error
+	Replay(w KeyValueWriter) error
 }
 
 // Batcher wraps the NewBatch method of a backing data store.