Add missing include to parse-duration.c.

[Ralf Wildenhues]

Hello Bruce,

ok to commit?  Seems pretty obvious.

Thanks,
Ralf

    Add missing include to parse-duration.c.
    
    * lib/parse-duration.c: #include "xalloc.h", for xstrdup.

diff --git a/lib/parse-duration.c b/lib/parse-duration.c
index 6487ba0..4c28349 100644
--- a/lib/parse-duration.c
+++ b/lib/parse-duration.c
@@ -23,6 +23,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include "xalloc.h"
 
 #include "parse-duration.h"