debian: set www-data group ownership

debian/flyers.postinst

@@ -4,7 +4,7 @@ set -e
 
 NAME="flyers"
 USER=$NAME
-GROUP=$NAME
+GROUP=www-data
 CONFIG_DIR="/etc/$NAME"
 MANAGE_SCRIPT="/usr/bin/$NAME-manage"
 
@@ -20,7 +20,8 @@ case "$1" in
     # ensure dirs ownership
     chown $USER:$GROUP /var/log/$NAME
     chown $USER:$GROUP /var/lib/$NAME/static
-    chown $USER:$GROUP /var/lib/$NAME/media
+    chown -R $USER:$GROUP /var/lib/$NAME/media
+    find /var/lib/$NAME/media -type d -exec chmod g+s {} \;
     # create a secret file
     SECRET_FILE=$CONFIG_DIR/secret
     if [ ! -f $SECRET_FILE ]; then