more improvements

[Peter Maas]

Hi,

just committed: checked save dialog for world files, some dialog
functions in dialogs to avoid code duplication. rur_start.py is a bit
shorter now.

Peter.

[Frederic Muller]

Great! Someone has just started to work on the Turkish translation
completion and as Chinese New Year is approaching I will have time to
put into the project again.

Thank you.

Fred