Move cgit_print_date into ui-shared, reuse in ui-summary

Signed-off-by: Lars Hjemli <hjemli@gmail.com>
diff --git a/cgit.h b/cgit.h
index a905e47..a54f2b5 100644
--- a/cgit.h
+++ b/cgit.h
@@ -85,6 +85,7 @@
 			  const char *query);
 
 extern void cgit_print_error(char *msg);
+extern void cgit_print_date(unsigned long secs);
 extern void cgit_print_docstart(char *title, struct cacheitem *item);
 extern void cgit_print_docend();
 extern void cgit_print_pageheader(char *title);