Manifest request frequency on live streams

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In live streams, subsequent manifest requests may return the same result. I.e., there is no new segment.

Sometimes this is due variable fragment duration (E.g., even if the average is 10 seconds, we see some 8 second fragments and some 12 second fragments). Other times, it is due to minor slowness ingesting the live stream.

In both these cases, a minor delay on ingest results an extra fragment duration worth buffer depletion. If there are no new segments in the manifest, we may be able to avoid a rebuffer by requesting the manifest again (shortly after the initial request).

As a quick fix we changed the following line:
https://github.com/mangui/flashls/blob/dev/src/org/mangui/hls/loader/LevelLoader.as#L247
to
var _reloadInterval : Number = _levels[level].averageduration **/2** ;

While probably not the most efficient solution, this fix reduced the percentage of rebuffered sessions by about 10% (taken from ~10,000 2 hour playbacks over a month).

Start at src/org/mangui/hls/loader/LevelLoader.as around line 247 and inspect how _reloadInterval is calculated and how repeated manifest results are handled. Reproduce the live-stream case where a manifest has no new segment, then determine whether a follow-up request can avoid buffer depletion without causing unnecessary requests; done means the rebuffer behavior improves without disrupting manifest loading.

Written by the indexing model from the issue text.