Syncing same named files

[turetske]

Currently, to avoid the case where two files have the same name and are synced but happen to have different contents can cause the synced file to become an amalgam of the two, the code will overwrite the file entirely during a sync if it's determined to be smaller than the original. We want to be smarter than this:

1. If the files are of differing sizes at ALL (larger or smaller), we should rewrite the file except in case 2)
2. As per the discussion in Sync and Recursive results #1638 - For internal uses of recursive sync (such as the plugin or on retries), we are okay if the transfer request restarts midway as there is no worry about collision of same named files with different contents