sequencer: left-trim the lines read from the script

Interactive rebase's scripts may be indented; We need to handle this
case, too, now that we prepare the sequencer to process interactive
rebases.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

sequencer.c

@@ -1158,6 +1158,9 @@ static int parse_insn_line(struct todo_item *item,
 	char *end_of_object_name;
 	int i, saved, status, padding;
 
+	/* left-trim */
+	bol += strspn(bol, " \t");
+
 	if (bol == eol || *bol == '\r' || *bol == comment_line_char) {
 		item->command = TODO_COMMENT;
 		item->commit = NULL;