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-Cleanup: make original comments doxygen compatible and remove/change outdated comments

industry_cmd.c

@@ -22,6 +22,7 @@
 #include "variables.h"
 #include "table/industry_land.h"
 #include "table/build_industry.h"
+#include "date.h"
 
 enum {
 	/* Max industries: 64000 (8 * 8000) */