Update Error 404 handling

[jleandroperez]

Error 404 (Not Found) is triggered when a local pending change is sent after the object itself got deleted in another device.

Current Behavior:
Local pending changes are disregarded, upon 404, and there are no recovery mechanisms in place.

Expected Behavior:

1. Ignore remote deletion messages, when the object has local pending changes
2. When error 404 is received, retry posting the full object.

[chengfred]

Clarification:
When doing #2 ( retry posting full object (by sending data in d)), remove sv field from change. Reason is: As server has already responded that this object no longer exists (404), specifying sv doesn't make sense anymore.