make Relation.replacejwithi operate on geometry like everyone else

While there is only one example of replacejwithi being called, it
is clear that the arguments are meant to be type Geometry, not
(Geometry, role) tuple.  So when replacing j with i, preserve the
existing role.

ogr2osm.py

@@ -293,7 +293,7 @@ def __init__(self):
         Geometry.__init__(self)
         self.members = []
     def replacejwithi(self, i, j):
-        self.members = [i if x == j else x for x in self.members]
+        self.members = [(i, x[1]) if x[0] == j else x for x in self.members]
         j.removeparent(self)
         i.addparent(self)