git: update to v2.0.3

This is slightly more involved than just bumping the version number
because it pulls in a change to convert the commit buffer to a slab,
removing the "buffer" field from "struct commit".  All sites that access
"commit->buffer" have been changed to use the new functions provided for
this purpose.

Signed-off-by: John Keeping <john@keeping.me.uk>

parsing.c

@@ -132,7 +132,8 @@ static const char *reencode(char **txt, const char *src_enc, const char *dst_enc
 struct commitinfo *cgit_parse_commit(struct commit *commit)
 {
 	struct commitinfo *ret;
-	const char *p = commit->buffer, *t;
+	const char *p = get_cached_commit_buffer(commit, NULL);
+	const char *t;
 
 	ret = xmalloc(sizeof(*ret));
 	ret->commit = commit;