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-Cleanup: make original comments doxygen compatible and remove/change outdated comments

graph_gui.c

@@ -14,6 +14,7 @@
 #include "strings.h"
 #include "debug.h"
 #include "variables.h"
+#include "date.h"
 
 static uint _legend_excludebits;
 static uint _legend_cargobits;