eth/downloader: concurrent receipt and state processing

core/block_processor.go

core/blockchain.go

core/blockchain_test.go

core/chain_makers.go

core/error.go

core/state/sync.go

core/state/sync_test.go

core/types/common.go

eth/downloader/downloader.go

eth/downloader/downloader_test.go

eth/downloader/queue.go

eth/downloader/types.go

ethdb/memory_database.go

trie/sync.go

trie/trie.go