fix(configure.ac): you must check for lib64
fix(configure.ac): you must check for lib64

this fixes the build for fedora 18

rackerlabs/openstack-guest-agents-unix,rackerlabs/openstack-guest-agents-unix,joejulian/openstack-guest-agents-unix,rackerlabs/openstack-guest-agents-unix,joejulian/openstack-guest-agents-unix,joejulian/openstack-guest-agents-unix