[PATCH] relation member sorting removes closed way

[cjw@…]

When the sort function of the relation editor is used on a relation with a closed way as first member, that member is removed from the relation. Example: add way 37858230 to relation 175519 (as first element) and try to sort.
The patch below fixes this problem by treating closed ways like nodes - the element is sorted as if the shared start/endpoint node of the way is the relation member. It also moves some duplicate code to a separate function.
​http://www.time4t.net/~cjw/josm/josm-relation-member-sort-closed-ways.patch

[Gubaer]

Applied in r1857