Scheduled Dispatch feature

Code is tested and run well on small-ish train network. Not tested extensively.

src/schdispatch.h

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+/* $Id$ */
+
+/*
+ * This file is part of OpenTTD.
+ * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
+ * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/** @file schdispatch.h Functions related to scheduled dispatch. */
+
+#ifndef SCHDISPATCH_H
+#define SCHDISPATCH_H
+
+#include "date_type.h"
+#include "vehicle_type.h"
+#include "settings_type.h"
+
+void ShowSchdispatchWindow(const Vehicle *v);
+
+/**
+ * Convert date and full date fraction to DateTicksScaled
+ * @param date  Current date
+ * @param full_date_fract  full date fraction, the number of scaled tick in current day
+ * @return DateTicksScaled for ths specified date/faction
+ */
+inline DateTicksScaled SchdispatchConvertToScaledTick(Date date, uint16 full_date_fract)
+{
+    return ((DateTicksScaled)date * DAY_TICKS) * _settings_game.economy.day_length_factor + full_date_fract;
+}
+
+/**
+ * Convert DateTicksScaled to date and full date fraction format
+ * @param tick DateTicksScaled to convert
+ * @param date  Point to date, for ourput
+ * @param full_date_fract  Pointer to uint16, for output
+ */
+inline void SchdispatchConvertToFullDateFract(DateTicksScaled tick, Date* date, uint16* full_date_fract)
+{
+    const int full_date = _settings_game.economy.day_length_factor * DAY_TICKS;
+    *date = tick / full_date;
+    *full_date_fract = tick % full_date;
+}
+
+#endif /* SCHDISPATCH_H */