trim: fix compilation error

[Bruno Haible]

This fixes a compilation error with IRIX 6.5 cc: strdup is declared in
<string.h>.

2008-04-11  Bruno Haible  <address@hidden>

        * lib/trim.c: Include <string.h>.

--- lib/trim.c.orig     2008-04-12 00:24:17.000000000 +0200
+++ lib/trim.c  2008-04-12 00:21:37.000000000 +0200
@@ -1,5 +1,5 @@
 /* Removes leading and/or trailing whitespaces
-   Copyright (C) 2006-2007 Free Software Foundation, Inc.
+   Copyright (C) 2006-2008 Free Software Foundation, Inc.
 
    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -22,6 +22,7 @@
 #include "trim.h"
 
 #include <ctype.h>
+#include <string.h>
 
 #if HAVE_MBRTOWC 
 # include <stddef.h>