Check for cancelled prior to doing IO
Check for cancelled prior to doing IO

So that IO that completes synchronously a lot will get the cancelled
notification.

This still does not check for cancellation for synchronous mode
(no IOManager), to avoid a larger behavior change that hasn't been
thought through yet.

Change-Id: Id911f12b1646980c4cea8894d72310bbba98b829
Reviewed-on: https://gerrit.dechocorp.com/11912
Reviewed-by: Jeremy Stanley <b3f594e10a9edcf5413cf1190121d45078c62290@mozy.com>

ccutrer/mordor,mozy/mordor,mozy/mordor,adfin/mordor,mtanski/mordor,cgaebel/mordor,mtanski/mordor,mtanski/mordor,ccutrer/mordor,adfin/mordor,cgaebel/mordor,mozy/mordor,ccutrer/mordor,adfin/mordor