Small fix for BSD.

Part of Code Review:
https://reviews.freebsd.org/D2055

Author:		Don Lewis (truckman at FreeBSD)

shell/source/unix/sysshell/recently_used_file_handler.cxx

@@ -40,6 +40,7 @@
 #include <algorithm>
 #include <functional>
 #include <string.h>
+#include <time.h>
 
 namespace /* private */ {
     //########################################