WIP
Fix tests
Rename IrminREST to IrminCRUD
Start testing the HTTP server and the CRUD interface

That's broken at the moment ...
CRUD over memory works

While CRUD over filesystem get mysterioulsy stucked ...
On some machines, seems that Lwt_unix.fork breaks the IO scheduler ...

To avoid that, use synchronized IO in the server process for the tests.

Very weird bug (I'm not sure I understand what happens exactly).
Implement S.list (return the available sub-paths)
Dummy stubs for import/export