Location dialog doesn't update the time zone

[alex-w]

Original report by Marcello Pietrobon: https://bugs.launchpad.net/stellarium/+bug/1712105

Using version 0.90.0.9767 trunk downloaded the 2017/08/20

When I change location from the location window the Time Zone is automatically adapting to the chosen location. This if I use the version 0.11,

but not if I use the 0.90.0.9767 trunk version.

[gzotti]

Final detail:

What Marcello wants (and I also see it would be nice) is clicking on the map and getting 
not only long/lat but also the correct timezone. This would require a polygon lookup 
(inside/outside testing) with a set of timezone-describing polygons, which we however 
do not have. (And they are frequently changing!)