Terrain/RasterWeather: LoadItem() returns RasterMap
Terrain/RasterWeather: make LoadItem() static
Terrain/RasterWeather: simplify the effective_weather_time loop
Terrain/RasterWeather: don't set the "reload" flag in SetTime()

This will be auto-detected by Reload().
Terrain/RasterWeather: add assertion to SetTime()

Obsoletes the std::min() call in Reload().
Terrain/RasterWeather: remove std::min() call from isWeatherAvailable()

Protected by assert().
Terrain/RasterWeather: make ExistsItem() static
Terrain/RasterWeather: move code to OpenArchive()
po: update Italian translation
po: update Croatian translation
Terrain/RasterWeather: add macros RASP_FILENAME, RASP_FORMAT