[omxplayer] Flush EOS message from queue to avoid it turning up after a seek

[popcornmix]

A GENERAL_EOS is queued when demuxer reaches EOF but playback may continue for several seconds.
It should be possible to seek backwards during this playback time, but the GENERAL_EOS may still be queued after flushing
and it unwantedly causes stream to stall after the seek. So flush these obsolete messages when flushing data packets

[popcornmix]

Ping @FernetMenta for sanity check.

[FernetMenta]

GENERAL_EOF seems pretty useless for dvdplayer, there is no real action triggered by this message. What does it do for OMXPlayer?

[popcornmix]

On GENERAL_EOF we send an EOS packet to decoder and then wait for the acknowledgement to come back so we know all frames have been flushed out.
However sending a spurious EOS packet (as occurs here when you seek back after an EOF) is bad and causes the clock to stall.

[FernetMenta]

So we send EOF because we want decoder to play out remaining packets, right? If this is the intent, the message is sent at a wrong point in time. Event the message name is wrong. What you really want is to instruct stream players to get finished.
Anyway, this is fine for dvd/omxplayer. Let's do a rework for VideoPlayer.

[popcornmix]

jenkins build this please