core/state: track all accounts in canon state

This change introduces a global, per-state cache that keeps account data
in the canon state. Thanks to @karalabe for lots of fixes.

internal/ethapi/api.go

@@ -1280,8 +1280,8 @@ func (api *PrivateDebugAPI) ChaindbProperty(property string) (string, error) {
 }
 
 // SetHead rewinds the head of the blockchain to a previous block.
-func (api *PrivateDebugAPI) SetHead(number uint64) {
-	api.b.SetHead(number)
+func (api *PrivateDebugAPI) SetHead(number rpc.HexNumber) {
+	api.b.SetHead(uint64(number.Int64()))
 }
 
 // PublicNetAPI offers network related RPC methods