[libyaml] Guard against overflows in indent and flow_level

https://bitbucket.org/xi/libyaml/commits/f859ed1eb757a3562b98a28a8ce69274bfd4b3f2
[libyaml] Fix CVE-2014-2525: Heap overflow when parsing YAML tags

The heap overflow is caused by not properly expanding a string before
writing to it in function yaml_parser_scan_uri_escapes in scanner.c.
[libyaml] Fix CVE-2014-9130: assert failure when processing wrapped strings

https://bitbucket.org/xi/libyaml/commits/2b9156756423e967cfd09a61d125d883fca6f4f2