The vio abstraction layer within csync is inneficient for the owncloud
use case because not all calls maps well to the POSIX interface. We can
be much more efficient by doing exactly what we need.
Also, this will allow us to scedule better the calls and possibly to use
threads.
SyncPrepare is when the folder class prepares the actual syncing,
i.e. does treewalks and runs the reconceiler in case of mirall. The actual
SyncRunning state will only be entered if there is actually anything to
sync.
Fixes#289