we only wait for the worker thread to remove the handle from its multi
and then signal us back. after that's done the transfer can be cleaned
up independently of the multi handle and no transfer progress is made.
we also no longer remove transfer items from multi handles in the item
destructor; only the worker thread can add a transfer and as such only
the worker thread should be responsible for removing them again later.
Change-Id: I6ff57bb5e7c1e91faf8657b257e73d6a72aa928e
eldritch horrors
60e984f0cf