Description of problem:
config comparison fails with "Fatal error in Python code occured [[6]]"

How reproducible:

Steps to Reproduce:
1. Schedule config comparison with channel where there is a directory.
2. Run rhn-check on client.
3. Check up2date logs for any of the client and we have:
------
Traceback (most recent call last):
  File "/usr/sbin/rhn_check", line 342, in __run_action
    (status, message, data) = CheckCli.__do_call(method, params, kwargs)
  File "/usr/sbin/rhn_check", line 335, in __do_call
    retval = method(*params, **kwargs)
  File "/usr/share/rhn/actions/configfiles.py", line 342, in diff
    diff = fp.diff(file)
  File "/usr/share/rhn/config_common/file_utils.py", line 128, in diff
    temp_file, temp_dirs = self.process(file_struct)
  File "/usr/share/rhn/config_common/file_utils.py", line 48, in process
    fullpath = directory + file_struct['path']
<type 'exceptions.TypeError'>: unsupported operand type(s) for +: 'NoneType' and 'str'
------

Actual results:
Task fails with "Fatal error in Python code occurred [[6]]".

Expected results:
Task should complete successfully.

Additional info:

Issue was introduced with changes for Bug 1177656.

Notes for QA:

* To reproduce this you will need not only files in config channel,
  but also directories.
* Please check that following 3 things work:
  * compare configs (with directories)
  * deploy configs (with directories)
  * fetch config channel with "rhncfg-manager download-channel"
    (with directories).