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/util/util.go

@@ -138,17 +138,12 @@ func DurWithin(
 	return val
 }
 
-// IsTty returns true if stdin is a terminal
-func IsTty() bool {
-	fd := os.Stdin.Fd()
+// IsTty returns true if the file is a terminal
+func IsTty(file *os.File) bool {
+	fd := file.Fd()
 	return isatty.IsTerminal(fd) || isatty.IsCygwinTerminal(fd)
 }
 
-// ToTty returns true if stdout is a terminal
-func ToTty() bool {
-	return isatty.IsTerminal(os.Stdout.Fd())
-}
-
 // Once returns a function that returns the specified boolean value only once
 func Once(nextResponse bool) func() bool {
 	state := nextResponse