Add support for XUrgency and matching _NET_WM_STATE_DEMANDS_ATTENTION

ewmh hint; urgencyborder is configurable.  The urgency flag will stick,
even while on a client in a non-viewable group, until the client
receives focus (where the border is reset).  Initial diff from Thomas
Adam with some changes/enhancements from me.

conf.c

@@ -88,6 +88,7 @@ conf_ignore(struct conf *c, char *val)
 static char *color_binds[] = {
 	"#CCCCCC",	/* CWM_COLOR_BORDER_ACTIVE */
 	"#666666",	/* CWM_COLOR_BORDER_INACTIVE */
+	"#FC8814",	/* CWM_COLOR_BORDER_URGENCY */
 	"blue",		/* CWM_COLOR_BORDER_GROUP */
 	"red",		/* CWM_COLOR_BORDER_UNGROUP */
 	"black",	/* CWM_COLOR_MENU_FG */
@@ -687,6 +688,7 @@ static char *ewmhints[] = {
 	"_NET_WM_STATE",
 	"_NET_WM_STATE_MAXIMIZED_VERT",
 	"_NET_WM_STATE_MAXIMIZED_HORZ",
+	"_NET_WM_STATE_DEMANDS_ATTENTION",
 };
 
 void