Take the metadata 'path' name instead of filename in change polling thread.
Take the metadata 'path' name instead of filename in change polling thread.

The problem with the file name is that it's lowercased, and thus doesn't
represent the 'true' file name as Onitu stores it. Fortunately, the 'path'
metadata key contains the unchanged filename.

- Store the revision after each upload end. It permits to keep Onitu's
  revision up-to-date and to not trigger a change detection in the change
  polling thread.

- Add more comments

- Do the prefix handling stuff once and for all instead of once per loop
  turn in the check polling thread

- More error handling

onitu/onitu,onitu/onitu,onitu/onitu