Description of problem: Executing pylint with the --disable-msg-cat command line option throws an exception as follows:

[shell]$ pylint --disable-msg-cat=warning,refactor,convention
Traceback (most recent call last):
  File "/usr/bin/pylint", line 4, in <module>
    lint.Run(sys.argv[1:])
  File "/usr/lib/python2.6/site-packages/pylint/lint.py", line 850, in __init__
    args = linter.load_command_line_configuration(args)
  File "/usr/lib/python2.6/site-packages/logilab/common/configuration.py", line 577, in load_command_line_configuration
    (options, args) = self._optik_parser.parse_args(args=args)
  File "/usr/lib/python2.6/optparse.py", line 1378, in parse_args
    stop = self._process_args(largs, rargs, values)
  File "/usr/lib/python2.6/optparse.py", line 1418, in _process_args
    self._process_long_opt(rargs, values)
  File "/usr/lib/python2.6/optparse.py", line 1493, in _process_long_opt
    option.process(opt, value, values, self)
  File "/usr/lib/python2.6/site-packages/logilab/common/optik_ext.py", line 239, in process
    self.action, self.dest, opt, value, values, parser)
  File "/usr/lib/python2.6/optparse.py", line 802, in take_action
    self.callback(self, opt, value, parser, *args, **kwargs)
  File "/usr/lib/python2.6/site-packages/logilab/common/configuration.py", line 454, in cb_set_provider_option
    self.global_set_option(opt_name, value)
  File "/usr/lib/python2.6/site-packages/logilab/common/configuration.py", line 458, in global_set_option
    self._all_options[opt_name].set_option(opt_name, value)
  File "/usr/lib/python2.6/site-packages/pylint/lint.py", line 318, in set_option
    meth(_id)
  File "/usr/lib/python2.6/site-packages/pylint/utils.py", line 193, in disable_message_category
    for catid in self._cat_ids(categories):
  File "/usr/lib/python2.6/site-packages/pylint/utils.py", line 187, in _cat_ids
    raise Exception('Unknown category identifier %s' % catid)
Exception: Unknown category identifier A

Version-Release number of selected component (if applicable): pylint-0.16.0-2.fc11.noarch


How reproducible: Allways


Steps to Reproduce:
1. Have pylint installed (yum install pylint) on latest rawhide
2. Execute it with the command line option --disable-msg-cat

pylint --disable-msg-cat=warning,refactor,convention

As an example

3. Watch it throw the exception
  
Actual results: Exception thrown

Expected results: Help message for pylint

Additional info: After debugging the problem, I realized that in the function _cat_ids, on utils.py, when the argument categories is a string instead of a list, the loop 

for catid in categories:

Will consider the string an array of characters. I made a patch that fixes the problem against the rawhide version of the package.