Fix auto-restore feature

Credit to @badjware for the solution

Fixes $45, #52, #54

CHANGELOG.md

@@ -1,6 +1,7 @@
 # Changelog
 
 ### master
+- bugfix: "auto restore" feature stopped working
 
 ### v3.1.0, 2015-03-14
 - properly quote scripts

continuum.tmux

@@ -43,15 +43,8 @@ add_resurrect_save_interpolation() {
 	fi
 }
 
-number_of_sessions() {
-	tmux list-sessions |
-		wc -l |
-		sed "s/ //g"
-}
-
-# when tmux server is first started, number of sessions is 0
 just_started_tmux_server() {
-	[ "$(number_of_sessions)" -eq 0 ]
+	[ "$(tmux display-message -p -F '#{start_time}')" -gt "$(($(date +%s)-10))" ]
 }
 
 start_auto_restore_in_background() {