Remove todo/question. We do want to check this.
Move these checks into the collection handler.
Enfore that we need to initialize a PARTIAL sync before we can call this.
Some logging.
Return early if no collections.
Do not take these values into account when comparing collections.
Don't initialize a full sync for a PING request. Kills the synckeys.
Don't clear all collections, just overwrite changed.
Smaller variable names.
Merge branch 'master' into eas
Logging
Only load from cache if we have an empty PING.
Handle a non empty PING, but with no FOLDERS.

This may happen rarely, but is used to update only the heartbeat interval.
Try to send more appropriate error codes.
This check does more harm than good, especially on iOS.
Ensure we send the proper response, and don't exit early in these cases.
No need to save the synckey, we use lastsynckey for this.
This is indeed true, remove this code.
Simplify
Only store the collection class, it's all we'll need this for.