Make --version report the active config file

This is useful for troubleshooting.

E.g.:

```
$ ansible-playbook --version
ansible-playbook 1.8 (make_hacking_env-setup_init_submodules 4530974b3b) last updated 2014/11/23 09:51:01 (GMT -700)
  lib/ansible/modules/core: (detached HEAD 19b328c4df) last updated 2014/11/23 09:44:44 (GMT -700)
  lib/ansible/modules/extras: (detached HEAD e64751b0eb) last updated 2014/11/23 09:48:22 (GMT -700)
  v2/ansible/modules/core: (detached HEAD cb69744bce) last updated 2014/11/23 09:48:34 (GMT -700)
  v2/ansible/modules/extras: (detached HEAD 8a4f07eecd) last updated 2014/11/23 09:48:45 (GMT -700)
  configured module search path = None
  config file = /etc/ansible/ansible.cfg
```

(Note the last line above).

Cc: @sontek, @sudarkoff