Changed context and ADDMOD, MULMOD

* Cleaned up VM execution. VM run now takes a context
* ADDMOD/MULMOD - removed incorrect cast

vm/virtual_machine.go

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