execute: Open separate handles to /dev/tty (in, out, err)

# This will no longer cause 'Vim: Warning: Output is not to a terminal'
  fzf --bind 'enter:execute:vim {}' > /tmp/foo

src/tui/ttyname_windows.go

@@ -2,13 +2,20 @@
 
 package tui
 
-import "os"
+import (
+	"os"
+)
 
 func ttyname() string {
 	return ""
 }
 
 // TtyIn on Windows returns os.Stdin
-func TtyIn() *os.File {
-	return os.Stdin
+func TtyIn() (*os.File, error) {
+	return os.Stdin, nil
+}
+
+// TtyIn on Windows returns nil
+func TtyOut() (*os.File, error) {
+	return nil, nil
 }