Comment 4 for bug 1604446

Part of this is similar to bug 1551686.

In addition the fix proposed in that bug (which won't help in this case, though) we have two options:
1) completely get rid of caching in location-service
2) When the client specifies maximumAge as 0, oxide should keep discarding any position update which carries an old timestamp

I think that implementing #2 is a good thing regardless of #1, so I'd suggest that at least this part would be fixed in Oxide.