use xstrdup instead of xmalloc + strcpy

This is one line shorter, and makes sure the length in the
malloc and copy steps match.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

http-walker.c

@@ -566,8 +566,7 @@ struct walker *get_http_walker(const char *url)
 	struct walker *walker = xmalloc(sizeof(struct walker));
 
 	data->alt = xmalloc(sizeof(*data->alt));
-	data->alt->base = xmalloc(strlen(url) + 1);
-	strcpy(data->alt->base, url);
+	data->alt->base = xstrdup(url);
 	for (s = data->alt->base + strlen(data->alt->base) - 1; *s == '/'; --s)
 		*s = 0;