CHANGE: streamline code getting rid of has_key() and useless tests and
branches on directory keys
FIX: change level of message in isEmpty() to verbose
FIX: attempt 10 times to schedule failed transfers
FIX: increment attempts to transfer files. Streamline some pieces of
code
FIX: improve log information
FIX: create a unique file name for proxy (including the request name)
FIX: create unique file name for proxy, adding the request name
FIX: ignore (and warn) for None files in subrequests