Drop having a separate type for style options and make them all strings,

which allows formats to be expanded. Any styles without a '#{' are still
validated when they are set but any with a '#{' are not. Formats are not
expanded usefully in many cases yet, that will be changed later.

To make this work, a few other changes:

- set-option -a with a style option automatically appends a ",".

- OSC 10 and 11 don't set the window-style option anymore, instead the
  fg and bg are stored in the pane struct and act as the defaults that
  can be overridden by window-style.

- status-fg and -bg now override status-style instead of trying to keep
  them in sync.

window.c

@@ -865,6 +865,9 @@ window_pane_create(struct window *w, u_int sx, u_int sy, u_int hlimit)
 	wp->fd = -1;
 	wp->event = NULL;
 
+	wp->fg = 8;
+	wp->bg = 8;
+
 	TAILQ_INIT(&wp->modes);
 
 	wp->layout_cell = NULL;
@@ -1096,6 +1099,7 @@ window_pane_set_mode(struct window_pane *wp, struct window_pane *swp,
 	wp->screen = wme->screen;
 	wp->flags |= (PANE_REDRAW|PANE_CHANGED);
 
+	server_redraw_window_borders(wp->window);
 	server_status_window(wp->window);
 	notify_pane("pane-mode-changed", wp);
 
@@ -1127,6 +1131,7 @@ window_pane_reset_mode(struct window_pane *wp)
 	}
 	wp->flags |= (PANE_REDRAW|PANE_CHANGED);
 
+	server_redraw_window_borders(wp->window);
 	server_status_window(wp->window);
 	notify_pane("pane-mode-changed", wp);
 }