Moved execution from vm to chain.

This moves call and create to the specified environments. Vms are no
longer re-used. Vm uses environment's Call(Code) and Create in order to
execute new contracts or transfer value between accounts.

State transition now uses the same mechanism described above.

vm/virtual_machine.go

@@ -1,8 +1,10 @@
 package vm
 
+import "math/big"
+
 type VirtualMachine interface {
 	Env() Environment
-	RunClosure(*Closure) ([]byte, error)
+	Run(me, caller ClosureRef, code []byte, value, gas, price *big.Int, data []byte) ([]byte, error)
 	Depth() int
 	Printf(string, ...interface{}) VirtualMachine
 	Endl() VirtualMachine