Preserve back_and_forth during restart

Add new key "previous_workspace_name" to the json dump of the root container.

src/ipc.c

@@ -651,6 +651,11 @@ void dump_node(yajl_gen gen, struct Con *con, bool inplace_restart) {
         y(integer, con->depth);
     }
 
+    if (inplace_restart && con->type == CT_ROOT && previous_workspace_name) {
+        ystr("previous_workspace_name");
+        ystr(previous_workspace_name);
+    }
+
     y(map_close);
 }
 

src/load_layout.c

@@ -420,6 +420,9 @@ static int json_string(void *ctx, const unsigned char *val, size_t len) {
             else if (strcasecmp(buf, "changed") == 0)
                 json_node->scratchpad_state = SCRATCHPAD_CHANGED;
             free(buf);
+        } else if (strcasecmp(last_key, "previous_workspace_name") == 0) {
+            FREE(previous_workspace_name);
+            previous_workspace_name = sstrndup((const char *)val, len);
         }
     }
     return 1;

src/workspace.c

@@ -11,9 +11,12 @@
 #include "all.h"
 #include "yajl_utils.h"
 
-/* Stores a copy of the name of the last used workspace for the workspace
- * back-and-forth switching. */
-static char *previous_workspace_name = NULL;
+/*
+ * Stores a copy of the name of the last used workspace for the workspace
+ * back-and-forth switching.
+ *
+ */
+char *previous_workspace_name = NULL;
 
 /* NULL-terminated list of workspace names (in order) extracted from
  * keybindings. */