Age che just like reserves (1% per 24 ETUs)

Factor aging out of age_levels() into new age_people().  Use it in
do_feed() to age che.

include/prototypes.h

@@ -704,6 +704,7 @@ extern int wu(natid, natid, char *, ...) ATTRIBUTE((format (printf, 3, 4)));
  * src/lib/update/ *.c
  */
 /* age.c */
+extern int age_people(int, int);
 extern void age_levels(int);
 /* anno.c */
 extern void delete_old_announcements(void);