Add doc id to oldDoc for ease-of-use in sync function

Add the doc id to oldDoc by prepending id property to incoming oldJson byte array.
Move oldDoc handling to sync_runner

Simplify the support for oldDoc id in the sync function by moving it to the sync_runner handling, instead of byte-level manipulation of raw oldDoc content.
Whitespace cleanup
Merge pull request #470 from couchbase/feature/issue_434

Add doc id to oldDoc for ease-of-use in sync function