- get rid of 'chapter merging'.

- get rid of 'chapter merging'.
- check for 'beginning of cell' before 'end of cell' so zero length cells don't
  make us advance to the next cell too early & fail to generate a chapter mark.
- don't read beyond the last cell of a title.
- if we get a read error just skip to the next vobu instead of giving up.
- fix the next_vobu mask (the top two bits have special meaning, not just
  the MSB), make the next vobu decision logic a bit closer to what a hardware
  dvd player uses (interpret the 2^30 bit as "look for a better vobu pointer
  in this navpack), make the 'end of vobu chain' recognition more robust.
- when we're searching for a navpack because we couldn't read the block
  'next_vobu' points to, recognize when we walk out of the current cell &
  just go to the next cell for this title.
- treat an internal vobu with a null prev_vobu pointer as if it were end-of-cell
  and advance to the next cell.
- use consistent case in log messages (always "dvd:" rather than a random mix
  of upper & lower case).

git-svn-id: svn://localhost/HandBrake/trunk@1215 b64f7644-9d1e-0410-96f1-a4d463321fa5