Fix bugs in user list

* URL is connection-dependent
* Open link in new window so as not to lose work
* Don't show undefined (fixes #302)

js/id/connection.js

@@ -138,6 +138,10 @@ iD.Connection = function() {
         });
     }
 
+    connection.userUrl = function(username) {
+        return apiURL + "/user/" + username;
+    };
+
     function tileAtZoom(t, distance) {
         var power = Math.pow(2, distance);
         return [

js/id/id.js

@@ -49,17 +49,18 @@ window.iD = function(container) {
             var users = {},
                 entities = map.history().graph().intersects(map.extent());
             for (var i in entities) {
-                users[entities[i].user] = true;
-                if (Object.keys(users).length > 10) break;
+                if (entities[i].user) {
+                    users[entities[i].user] = true;
+                    if (Object.keys(users).length > 10) break;
+                }
             }
             var u = Object.keys(users);
             var l = d3.select('#user-list')
                 .selectAll('a.user-link').data(u);
             l.enter().append('a')
                 .attr('class', 'user-link')
-                .attr('href', function(d) {
-                    return 'http://api06.dev.openstreetmap.org/user/' + d;
-                })
+                .attr('href', function(d) { return connection.userUrl(d); })
+                .attr('target', '_blank')
                 .text(String);
             l.exit().remove();
         }, 1000);