HipHop fails to start with error: Unable to find/load systemlib.php

This seems to be caused by trying to enable Jit compiliation, as happens when setting loglevel to None or Error.

To replicate on the dev server:

```
vagrant@precise64:~$ grunt rebuild
Running "clean:test" (clean) task
...snip...
Running "compile-buildpack" task
...snip...
-----> Done with compile

Done, without errors.

vagrant@precise64:~$ cd ~/dist
vagrant@precise64:~/dist$ bin/start.sh 4567 Error
-----> BASE_DIR: /home/vagrant/dist
-----> Writing config files...
-----> Using LOGLEVEL: Error [options: None | Error (default) | Warning | Info | Verbose ]
-----> Starting HipHop VM v2.0.0 (rel)
Unable to find/load systemlib.php
```