Description of problem:
attempt to list config files in command line, ends with traceback due unavailable display. not 'tracebacking' when display is available, but output is text only, no gui appeared. seems nonsense to import pygtk stuff in list_config, when gui is not needed.

Version-Release number of selected component (if applicable):
0.11.1

How reproducible:
alway

Steps to Reproduce:
1. install tuna
2. unset DISPLAY
3. run tuna -l
4. check output

Actual results:
[root@mrg-qe-15 ~]# tuna -l

Traceback (most recent call last):
  File "/usr/bin/tuna", line 647, in <module>
    main()
  File "/usr/bin/tuna", line 488, in main
    list_config()
  File "/usr/bin/tuna", line 440, in list_config
    from tuna.config import Config
  File "/usr/lib/python2.7/site-packages/tuna/config.py", line 2, in <module>
    import sys, gtk, pygtk
  File "/usr/lib64/python2.7/site-packages/gtk-2.0/gtk/__init__.py", line 64, in <module>
    _init()
  File "/usr/lib64/python2.7/site-packages/gtk-2.0/gtk/__init__.py", line 52, in _init
    _gtk.init_check()
RuntimeError: could not open display


Expected results:

[root@mrg-qe-15 ~]# tuna -l
Preloaded config files:
example.conf

Additional info: