Add reporting of fifo fullness for use with hdmi_status_show
that stops the stray message entering the Q, which causes it to
immediately try and go normal speed when it should be buffering.

Strictly this is not quite right, it then results in some Put() calls
to the Q befores its init'd, but its those messages that caused the
initial (wrong) set speed etc... Really it needs fixing properly, but
this at least brings omxplayer into line with the other players.
Expose GetAudioRenderingLatency
Add OMXLateCount to query if packets have arrived late
Add more debug logging
Use CurrentHostCounter consistently
Use correct size when determining fifo has space in it
Always acquire lock when using OMXMediaTime
Avoid 500ms offset when rendering subtitles