linux: allow root user to raise priority
Merge pull request #3840 from FernetMenta/linux

linux: allow root user to raise priority
videoplayer: adapt lateness detection and dropping to buffering
video player: present correct pts to user for a/v sync (after buffering in renderer)
videoplayer: some rework and documentation
renderer: bump buffers to 5
videoplayer: update frametime, it might change due to fps detection
videoplayer: give streams with invalid fps a chance for fps detection
dvdplayer: allow rewinding at end of stream, do a seek after rewind
X11: ditch SDL for video and window events
X11: Add xbmc icon
X11: add SDL joystick until we have a better solution
X11: factor out code handling device reset notification
X11: move xrandr events to WinEventsX11
xrandr: remove method RestoreState
xrandr: observe orientation
xrandr: allow getting info for multiple screen's

Refactored by: Joakim Plate <elupus@xbmc.org>
X11: fix multi-head setups
X11: remove all DefaultScreen and RootWindow macros
X11: remove all DefaultScreen and RootWindow macros (VideoRefClock)

Note this is on a separate display connection.