Don't bother overwaiting in waitForDone(), if it was done at one point
after it was called we can return true. And do not stop threads recently
awakened by a startThread call as they have tasks to do.
Make allowing at least one thread regardless of reservation more
standard instead of hacked in certain places.
Pick-to: 6.2
Change-Id: I304bcdc5822f440d5e72fc33ba2aa1678c9ba0d0
Reviewed-by: David Faure <david.faure@kdab.com>