use vendered libyajl2 if we find it installed
use vendered libyajl2 if we find it installed

- extconf.rb must be smart enough to figure out if the system
  libyajl2 is usable or not, if it isn't usable, it will install
  the vendered lib, which we always use

h4ck3rm1k3/ffi-yajl,chef/ffi-yajl,kou/ffi-yajl,kou/ffi-yajl,chef/ffi-yajl,h4ck3rm1k3/ffi-yajl,chef/ffi-yajl,kou/ffi-yajl,h4ck3rm1k3/ffi-yajl