#2 to back up selected Title Track(TT_SRPT) instead of VTS

[Yishin Li]

divo was designed to back up selected VTS, which may
includes multiple Title Tracks. For some DVDs, ex:
MALENA, the major feature occupies entire VTS. The old
design was targeting this kind of DVDs.

However, for some DVDs, such as HEAT, the major
feature(Title Track) was mixed with other Title Tracks
in the same VTS. This could be a conflict as divo was
designed to back up portion of a DVD in order to shrink
image size.

Therefore, I'll have to revise the code so that divo
will only back up selected Title Track instead of whole
VTS.