Revisit zsh integration

zsh's antisocial behaviour was fairly promptly fixed (thanks to
Stephane Chazelas and his patience).

zle-line-init and zle-line-reset seem to be user-defined widgets
and the order inverted.  Put zle-line-init before reset-prompt
because some people do weird things in there.

README.adoc

@@ -54,7 +54,7 @@ To start using this navigator, put the following in your '.zshrc':
 
 ----
 sdn-navigate () {
-  # ... possibly zle-line-init
+  # ... possibly zle-line-finish
   while eval "`sdn "$BUFFER" "$CURSOR"`"; do
     [ -z "$cd" ] || cd "$cd"
     [ -z "$insert" ] || LBUFFER="$LBUFFER$insert "
@@ -66,8 +66,8 @@ sdn-navigate () {
 
     eval "exec </dev/tty; $helper" || break
   done
+  # ... possibly zle-line-init
   zle reset-prompt
-  # ... possibly zle-line-finish
 }
 zle -N sdn-navigate
 bindkey '\eo' sdn-navigate

sdn.cpp

@@ -1654,7 +1654,8 @@ fun save_config () {
 }
 
 int main (int argc, char *argv[]) {
-	// That bitch zle closes stdin before exec without redirection
+	// zsh before 5.4 may close stdin before exec without redirection,
+	// since then it redirects stdin to /dev/null
 	(void) close (STDIN_FILENO);
 	if (open ("/dev/tty", O_RDWR)) {
 		cerr << "cannot open tty" << endl;