fs.CountError is called when an error is encountered. The method was
calling GlobalStats().Error(err) which incremented the error at the
global stats level. This led to calls to core/stats with group= filter
returning an error count of 0 even if errors actually occured.
This change requires the context to be provided when calling
fs.CountError. Doing so, we can retrieve the correct StatsInfo to
increment the errors from.
Fixes#5865
Before this change the code which summed up the existing transfers
over all the stats groups forgot to add the old transfer time and old
transfers in.
This meant that the speed and elapsedTime got increasingly inaccurate
over time due to the transfers being culled from the list but their
time not being accounted for.
This change adds the old transfers into the sum which fixes the
problem.
This was only a problem over the rc.
Fixes#4569
