Save grouped sessions

Grouped sessions are session started with the command
`tmux new-session -t <existing-session-name>`

Those sessions share the panes and windows with the existing, original
session.
We're making sure to identify and save grouped sessions.
On the other hand, we don't want to save panes and windows twice

scripts/helpers.sh

@@ -3,6 +3,8 @@ resurrect_dir_option="@resurrect-dir"
 
 SUPPORTED_VERSION="1.9"
 
+d=$'\t'
+
 # helper functions
 get_tmux_option() {
 	local option="$1"
@@ -54,6 +56,16 @@ save_bash_history_option_on() {
 	[ "$option" == "on" ]
 }
 
+get_grouped_sessions() {
+	local grouped_sessions_dump="$1"
+	export GROUPED_SESSIONS="${d}$(echo "$grouped_sessions_dump" | cut -f2 -d"${d}" | tr "\\n" "${d}")"
+}
+
+is_session_grouped() {
+	local session_name="$1"
+	[[ "$GROUPED_SESSIONS" == *"${d}${session_name}${d}"* ]]
+}
+
 # path helpers
 
 resurrect_dir() {