Do not take the initial format set to TIME too seriously when we
haven't got any newsegment event yet. If it is the first segment
received, switch our internal segment tracker to the event format
Segments, upstream seeks and flushes. Adding the following checks:
* A flush stop is expected after a flush start
* After a seek, the flushes/segment seqnum should be the same as the seek
The base class adds a 'object' property to hold the monitored object,
it can only be set on construction. Also the constructor now
automatically calls the element set up