(svn r5887) -Cleanup: move date related functions, defines and variables to date.[ch]

-Cleanup: fix whitespace related coding style issues in date.[ch]
-Cleanup: make original comments doxygen compatible and remove/change outdated comments

ship_cmd.c

@@ -25,6 +25,7 @@
 #include "debug.h"
 #include "newgrf_callbacks.h"
 #include "newgrf_text.h"
+#include "date.h"
 
 static const uint16 _ship_sprites[] = {0x0E5D, 0x0E55, 0x0E65, 0x0E6D};
 static const byte _ship_sometracks[4] = {0x19, 0x16, 0x25, 0x2A};