Comment 1 for bug 299967

Here is a patch to fix the reported issues above.
Explanations on the modifications:

=== modified file 'src/nssbackup/util/__init__.py':

* adding new functions to unify checking of expressions (maybe it is useful for further versions to create somekind of ConfigurationHandler class to encapsulate reading configuration files, checking of configuration values and setting of new ones - so this is a bugfix only for the current release candidate version)

=== modified file 'src/nssbackup/ui/SBConfigGTK.py':

* adding a method for showing a dialogbox containing an errormessage

* the regular expressions from the configuration file were checked before they are added to any lists; if they are invalid they were removed and the users gets informed. This fixes issue 4).

* if a regular expression is added to the configuration, the resulting line gets stripped off leading and trailing ',' to avoid to unwanted adding of an empty expression

* in method 'on_ex_delregex_clicked': the removal of an expression is done by the function mentioned above. The last expression didn't had a leading comma, so it was not removed. This fixes issue 3).

* in method 'cell_regex_edited_callback': it was possible to clear the expression and therefore an empty expression was stored. The fix now checks not only for a valid expression but additionally for a not empty expression. This fixes issue 1).

* while checking regular expression only 're.error' were catched now.

=== modified file 'src/nssbackup/managers/BackupManager.py':

* while reading the configuration it is checked whether the expression is not empty and valid. If so it is added otherwise output a log message. This fixes issue 2).

=== modified file 'src/nssbackup/managers/SnapshotManager.py'

* string formatting was errornous. Fixed without changing the content of translated string. This fixes bug Bug #299964: Exception 'TypeError' is raised if an error occurs while pulling a snapshot.