Allow forward/back skip buttons and trickplay to navigate between timeshift events

[prl]

Allow the skip buttons, FF/REW and other trickplay modes to skip back from the start of a timeshift event to the end of the previous one, and to skip forward from the end of a timeshift event to the start of the next one.

This would give a more continuous "feel" to the timeshift buffer.

The functions of PREV and NEXT to jump between timeshift events should remain.

[Wade Coxon]

Another related enhancement for this same request:

If in timeshift and trick playing at FF speeds and playback catches up with Live TV (runs out of timeshift buffer), then playback should either: a) drop out of timeshift mode and return to Live TV; or b) drop out of FF and resume normal playback speed.

Similar to the above, if a user uses the skip forward button and reaches the Live TV position, or uses the NEXT> button while timeshifting in the last event in the timeshift buffer.