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>

line-log.c

@@ -520,7 +520,7 @@ static void fill_line_ends(struct diff_filespec *spec, long *lines,
 	char *data = NULL;
 
 	if (diff_populate_filespec(spec, 0))
-		die("Cannot read blob %s", sha1_to_hex(spec->sha1));
+		die("Cannot read blob %s", oid_to_hex(&spec->oid));
 
 	ALLOC_ARRAY(ends, size);
 	ends[cur++] = 0;