using a lock and I'm not very much in favor of a global one.
* Added "finished" callback to IORequest.
* IOOperation::Finish() no longer invokes its parent request's
ChunkFinished(). The finisher does this instead. ChunkFinished()
can optionally remove the chunk from the parent.
* Added IORequest::Wait() which waits for the completion of the request.
* Introduced IORequestChunk::ResetStatus() to make setting the status to
"pending" somewhat more explicit.
* Implemented the missing IOScheduler::SetCallback() methods.
* The NotifyAll() calls on the IOScheduler's condition variables were
missing, so it just waited forever.
* Added some more debug output.
git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@26597 a95241bf-73f2-0310-859d-f6bbb57e9c96