Fixed VBeam emulation in interlaced mode, removing the hacks in the audio timing.
Fixed VBeam emulation in progressive scan mode.
Retained the old VBeam speed hack.  This option has now been switched so that the accurate behaviour is on by default and the speed hack (inaccurate behaviour) is enabled when the option is checked.
Renamed the VBeam variable for clarity.
Merge branch 'VBeam-fix'

* VBeam-fix:
  Renamed the VBeam variable for clarity.
  Fixed VBeam emulation in interlaced mode, removing the hacks in the audio timing. Fixed VBeam emulation in progressive scan mode. Retained the old VBeam speed hack.  This option has now been switched so that the accurate behaviour is on by default and the speed hack (inaccurate behaviour) is enabled when the option is checked.