(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-Cleanup: make original comments doxygen compatible and remove/change outdated comments

town_cmd.c

@@ -26,6 +26,7 @@
 #include "water_map.h"
 #include "variables.h"
 #include "bridge.h"
+#include "date.h"
 #include "table/town_land.h"
 
 enum {