diff: convert struct diff_filespec to struct object_id

Convert struct diff_filespec's sha1 member to use a struct object_id
called "oid" instead.  The following Coccinelle semantic patch was used
to implement this, followed by the transformations in object_id.cocci:

@@
struct diff_filespec o;
@@
- o.sha1
+ o.oid.hash

@@
struct diff_filespec *p;
@@
- p->sha1
+ p->oid.hash

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diffcore-break.c

@@ -58,7 +58,7 @@ static int should_break(struct diff_filespec *src,
 	}
 
 	if (src->sha1_valid && dst->sha1_valid &&
-	    !hashcmp(src->sha1, dst->sha1))
+	    !oidcmp(&src->oid, &dst->oid))
 		return 0; /* they are the same */
 
 	if (diff_populate_filespec(src, 0) || diff_populate_filespec(dst, 0))