libyaml 0.1.6

Closes a security vulnerability:
http://www.ocert.org/advisories/ocert-2014-003.html
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2014-2525
libyaml: update 0.1.6 bottle.

Closes #27923.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>
Fix Keg#find so we don't have to deal with it everywhere

lol inheritance
Put constant strings in a constant
use File.symlink
we alway pass pathnames
rescue specific exceptions
move make_relative_symlink error handling into keg and adjust callers
use actual keg name
src is already absolute
wip