Fixed AttributeError in Refit

Before these changes I was getting this:

131113-10:53:15,735 workflow INFO:
	 Running: 3drefit -deoblique /tmp/tmp0nwzz7/func_preproc/func_deoblique/rest_calc.nii.gz...

.../lib/python2.7/site-packages/nipype/interfaces/afni/preprocess.py", line 200, in _list_outputs
    self.outputs["out_file"] = os.path.abspath(self.inputs.in_file)
AttributeError: 'Refit' object has no attribute 'outputs'
Interface Refit failed to run.

The changes allow the workflow to complete successfully. Let me know your thoughts.