Optimize Next implementation

Once the program detects that we have stepped into another function,
we simply calculate the return address and then set a breakpoint and
continue to that location, avoiding numerous syscalls.

proctl/proctl_test.go

@@ -2,7 +2,6 @@ package proctl_test
 
 import (
 	"bytes"
-
 	"path/filepath"
 	"syscall"
 	"testing"