Bugfix: Obey workspace_layout when re-inserting floating containers (+test) (Thanks aksr)

The code wasn’t using con_attach and therefore didn’t obey workspace_layout.

Fixes: #631

src/floating.c

@@ -238,11 +238,10 @@ void floating_disable(Con *con, bool automatic) {
     /* con_fix_percent will adjust the percent value */
     con->percent = 0.0;
 
-    TAILQ_INSERT_TAIL(&(con->parent->nodes_head), con, nodes);
-    TAILQ_INSERT_TAIL(&(con->parent->focus_head), con, focused);
-
     con->floating = FLOATING_USER_OFF;
 
+    con_attach(con, con->parent, false);
+
     con_fix_percent(con->parent);
     // TODO: don’t influence focus handling when Con was not focused before.
     con_focus(con);