vtrackinfo file versioning

[cassella]

current version and "first version that can read this"

• eg, when we can do VFRAMES=1-500,2000-3000,600-1500
• some of the others below
• versioning on both .vtrackinfo files and VALBUMs.
  VTRACKINFOVERSION=0
  VALBUMVERSION=0
  ...
  VNEWALBUM
  VALBUMVERSION=1
  new_feature
  ...
  VNEWALBUM
  VALBUMVERSION=0
  ...