blame: read custom grafts given by -S before calling setup_revisions()

setup_revisions() while getting the command line arguments parses the
given commits from the command line, which means their direct parents will
not be rewritten by the custom graft file.

Call read_ancestry() early to work around this issue.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-blame.c

@@ -2346,6 +2346,10 @@ int cmd_blame(int argc, const char **argv, const char *prefix)
 parse_done:
 	argc = parse_options_end(&ctx);
 
+	if (revs_file && read_ancestry(revs_file))
+		die("reading graft file %s failed: %s",
+		    revs_file, strerror(errno));
+
 	if (DIFF_OPT_TST(&revs.diffopt, FIND_COPIES_HARDER))
 		opt |= (PICKAXE_BLAME_COPY | PICKAXE_BLAME_MOVE |
 			PICKAXE_BLAME_COPY_HARDER);
@@ -2484,10 +2488,6 @@ parse_done:
 	sb.ent = ent;
 	sb.path = path;
 
-	if (revs_file && read_ancestry(revs_file))
-		die("reading graft file %s failed: %s",
-		    revs_file, strerror(errno));
-
 	read_mailmap(&mailmap, ".mailmap", NULL);
 
 	if (!incremental)