Set title via atomic print statement (#399)

Previously, `setopt xtrace` would produce terminal bell rings (by \a)
whenever the title was set because of debug output between print
statements. As a result, the title was not set and the terminal bell
rang.

This change also utilizes the improved ssh connection detection to
provide hostname in title when changing user on remote machines.

pure.zsh

@@ -63,18 +63,22 @@ prompt_pure_set_title() {
 		/dev/ttyS[0-9]*) return;;
 	esac
 
-	# tell the terminal we are setting the title
-	print -n '\e]0;'
-	# show hostname if connected through ssh
-	[[ -n $SSH_CONNECTION ]] && print -Pn '(%m) '
+	# Show hostname if connected via ssh.
+	local hostname=
+	if [[ -n $prompt_pure_state[username] ]]; then
+		# Expand in-place in case ignore-escape is used.
+		hostname="${(%):-(%m) }"
+	fi
+
+	local -a opts
 	case $1 in
-		expand-prompt)
-			print -Pn $2;;
-		ignore-escape)
-			print -rn $2;;
+		expand-prompt) opts=(-P);;
+		ignore-escape) opts=(-r);;
 	esac
-	# end set title
-	print -n '\a'
+
+	# Set title atomically in one print statement so that it works
+	# when XTRACE is enabled.
+	print -n $opts $'\e]0;'${hostname}${2}$'\a'
 }
 
 prompt_pure_preexec() {