Fix another compiler warning from the Export via GPSBabel work
Fix needing to calculate bounds of *both* tracks when a track is split via the marker.
[QA] Remove redundant GTK checks for > 2.10, since we need 2.16.
RedNotebook 1.7.3+ integration to open the diary program on a specific date.

It opens the diary program on the day of the selected track or waypoint.

Requires RedNotebook 1.7.3+ to support opening on the specified date.
This is only made available if an appropriate version of RedNotebook is detected.