In 53a1a0e3ef we introduced a problem where if there was an
error on the file being transferred then the file was re-opened and
the old one wasn't closed.
This was partially fixed in bfbddab46b however this didn't
address the case of the old file being closed.
This is now fixed by
- marking the file as open again in UpdateReader
- moving the stopping the accounting machinery to a new method Done
Before this change, using -P occasionally deadlocked on the Transfer
mutex when Transfer.Done() was called with a non nil error and the
StatsInfo mutex since they mutually call each other.
This was fixed by making sure that the Transfer mutex is always
released before calling any StatsInfo methods.
This improves on: 6f87267b34Fixes#3505
Before this change, using -P occasionally deadlocked on the transfer
mutex and the stats mutex since they call each other via the progress
printing.
This is fixed by shortening the locking windows and converting the
mutex to a RW mutex.
This is done to make clear ownership over accounting object and prepare
for removing global stats object.
Stats elapsed time calculation has been altered to account for actual
transfer time instead of stats creation time.
