Fix AirTunes pts accuracy
[rbp/omxplayer] Fix audio volume jumps when switching tracks

When the global volume has been set low, and a sequence of tracks are being played, there are complaints of occasional jumps to full volume.
This is down to a race condition where the volume request can arrive at OMXAudio before it has been initialised.
The fix is simple, don't send the volume change until m_CurrentAudio.started.
Merge pull request #2641 from popcornmix/fix_volume_jump

[rbp/omxplayer] Fix audio volume jumps when switching tracks
Merge pull request #2625 from hmis/AirTunes_pts

Fix AirTunes pts accuracy
[libdvd] - added missing patches
[Fix] http protocol options seekable=0 now finally works.
Merge pull request #2644 from ulion/fix_seekable_protocol_option

[Fix] http protocol options seekable=0 now finally works.
GUIFadeLabelControl: fix control being marked as dirty when label stays empty

If used infolabel will return empty string on first use, m_shortText will never be evaluated. If m_shortText is set to false control is marked as dirty so if used infolabel is empty control will be wrongly marked as dirty.
VideoRenerers: add buffering
add buffering for GLES
WinRenderer: add buffering
DXVA: activate buffering in renderer
linuxrenderer: delete all textures on reconfigure
drop frame counter in application, ask render manager instead
vaapi: adopt to buffering in renderer
add buffering - some documentation
move NUM_BUFFERS up to BaseRenderer.h
OverlayRenderer: align buffers with index in renderManager
add buffering - submit absolute time to render buffers
RenderManager: some rework to buffering