Merge branch 'day_length' into jgrpp

# Conflicts:
#	src/saveload/afterload.cpp

src/saveload/afterload.cpp

@@ -759,6 +759,11 @@ bool AfterLoadGame()
 		assert(_tick_skip_counter < _settings_game.economy.day_length_factor);
 	}
 
+	/* Set day length factor to 1 if loading a pre day length savegame */
+	if (SlXvIsFeatureMissing(XSLFI_VARIABLE_DAY_LENGTH) && SlXvIsFeatureMissing(XSLFI_SPRINGPP)) {
+		_settings_game.economy.day_length_factor = 1;
+	}
+
 	/* Update current year
 	 * must be done before loading sprites as some newgrfs check it */
 	SetDate(_date, _date_fract);

src/saveload/extended_ver_sl.cpp

@@ -136,6 +136,7 @@ void SlXvResetState()
 {
 	_sl_is_ext_version = false;
 	_sl_is_faked_ext = false;
+	_sl_xv_discardable_chunk_ids.clear();
 	memset(_sl_xv_feature_versions, 0, sizeof(_sl_xv_feature_versions));
 }