When making floating cons tiling, re-insert next to the next focused *tiling* con (Thanks mseed)

Fixes: #337 and #350

include/con.h

@@ -167,6 +167,16 @@ Con *con_get_next(Con *con, char way, orientation_t orientation);
  */
 Con *con_descend_focused(Con *con);
 
+/**
+ * Returns the focused con inside this client, descending the tree as far as
+ * possible. This comes in handy when attaching a con to a workspace at the
+ * currently focused position, for example.
+ *
+ * Works like con_descend_focused but considers only tiling cons.
+ *
+ */
+Con *con_descend_tiling_focused(Con *con);
+
 /**
  * Returns a "relative" Rect which contains the amount of pixels that need to
  * be added to the original Rect to get the final position (obviously the