add i3-nagbar. tells you about config file errors (for example)

include/config.h

@@ -32,6 +32,8 @@ extern SLIST_HEAD(modes_head, Mode) modes;
  *
  */
 struct context {
+        bool has_errors;
+
         int line_number;
         char *line_copy;
         const char *filename;
@@ -190,6 +192,17 @@ void switch_mode(const char *new_mode);
  */
 Binding *get_binding(uint16_t modifiers, xcb_keycode_t keycode);
 
+/**
+ * Kills the configerror i3-nagbar process, if any.
+ *
+ * Called when reloading/restarting.
+ *
+ * If wait_for_it is set (restarting), this function will waitpid(), otherwise,
+ * ev is assumed to handle it (reloading).
+ *
+ */
+void kill_configerror_nagbar(bool wait_for_it);
+
 /* prototype for src/cfgparse.y */
 void parse_file(const char *f);