rosetta-approve-imports.py repeats warnings making output unreadable

[Stuart Bishop]

Warning messages like the following can be repeated dozens of times in a run:

2009-10-10 02:53:18 WARNING Found multiple templates with translation domain 'kioexec'. There should be only one.

We should maintain a list of warnings emitted so far and stop repeating ourselves. This will make the output readable and make it easier to deal with the warnings.

[Jeroen T. Vermeulen (jtv)]

We also have bug 448019, which is really easy to fix. I think it'll massively shorten our response time to these conflicts, and so vastly reduce the number of log messages. The extra bit of intelligence proposed here may turn out to be unnecessary.