Every sync is an initial sync

Somehow the servers are not getting our sync_token, and so they are treating every /sync as if it were an initial /sync, rather than an incremental one.

This is causing unnecessary load on the servers, and it is bloating the sync responses -- we're seeing averages of 250-350 KB!

We thought we had fixed this before the Nov 14 tests, but apparently my "fix" didn't quite work.