libyaml: Patch to fix CVE-2013-6393.

I used all the patches from the RedHat bugzilla thread at https://bugzilla.redhat.com/show_bug.cgi?id=1033990 .  Hopefully they fix the problem.

I haven't really tested this.  On my system this only causes LaTeX to be rebuilt, and I am guessing it is only some obscure LaTeX package that uses yaml.