Install libyaml from source to address CVE-2013-6393.

Versions of libyaml < 0.1.5 are vulnerable to CVE-2013-6393. Ubuntu
10.04 lists libyaml as unsupported and will not be releasing a patched
version. As a result we need to install libyaml from source rather than
using the system provided libyaml.
Merge pull request #189 from bryantraywick/install-libyaml-from-source

Install libyaml from source to address CVE-2013-6393.