#320 RZX RollbackTo preview

[Sergio Baldoví]

The attached patch (GTK UI) improves the functionality of rollbacking to a previous point when recording RZX files. The current 'Rollback To' dialog shows a list with seconds where a snapshot has been stored. In my opinion there are some points to improve:

• When a point is later than 60 seconds, it's hard to assimilate that amount in the mind. A recording might be very long so a HH:MM:SS time format would be more friendly. Fractions of seconds don't give any valuable information.
• Who save the snapshot. They come from two sources: saved by the user and auto-saved. An indicator would be useful because the former could be more valuable.
• I can remember what happened a few seconds ago but it's hard for 5 minutes ago, though. If I wrongly rollback to a point, the later input will be destroyed. A screen preview extracted from a snapshot might give an accurate clue about the point.
• The rollback list had the last input block. That's an invalid rollback point and gives a nice error if the user selects it.
• The dialog is higher than screen when there are too many points. A scrollbar is needed.

I'll commit this patch in a few weeks barring objections.

get_rollback_list() will break compatibility in other UIs but it's not hard to adapt the code to the new structure of data:

• Widget UI's don't have an implementation for 'Rollback To' (nothing to fix).
• I'll check the win32 UI.
• For Mac OS X port the ball is in Fred's court.