parsing YAML tags.
Also apply a patch for hardenning the guards againt the issue
The only user in base in yaml is pkg(7) which uses the library a way that it is not affected
Submitted by: delphij
Obtained from: https://bugzilla.redhat.com/show_bug.cgi?id=1033990
MFC after: 3 days
Security: CVE-2013-6393
LibYAML is a YAML 1.1 parser and emitter under MIT license which will
soon be used by the pkg boostrap (usr.bin/pkg) and bhyve
Reviewed by: roberto, antoine