Do not use memcmp(sha1_1, sha1_2, 20) with hardcoded length.

Introduces global inline:

	hashcmp(const unsigned char *sha1, const unsigned char *sha2)

Uses memcmp for comparison and returns the result based on the length of
the hash name (a future runtime decision).

Acked-by: Alex Riesen <raa.lkml@gmail.com>
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>

ssh-fetch.c

@@ -67,7 +67,7 @@ int fetch(unsigned char *sha1)
 	signed char remote;
 	struct object_list *temp;
 
-	if (memcmp(sha1, in_transit->item->sha1, 20)) {
+	if (hashcmp(sha1, in_transit->item->sha1)) {
 		/* we must have already fetched it to clean the queue */
 		return has_sha1_file(sha1) ? 0 : -1;
 	}