presence: Use people.is_my_user_id() for check.

This is the preferred way to check that a user
id belongs to the current user.

We have a recent bug where the current user's
circle doesn't turn green right away.  It's not
clear this is the fix, though.  (It's hard to
repro locally.)

static/js/presence.js

@@ -33,7 +33,7 @@ exports.is_active = function (user_id) {
 };
 
 exports.get_status = function (user_id) {
-    if (user_id === page_params.user_id) {
+    if (people.is_my_user_id(user_id)) {
         return "active";
     }
     if (user_id in exports.presence_info) {