Restore a helper-function for testing.

This was in coherence.extern.louie some-when already but got lost.
Fix: Need to upper-case log-level names when passing to std-logging-module.
Add test-case for browsing a non existing object.
Fix: test-cases hang when browsing non-existing object.
Add test-case for fs_storage backend.
Fix: self.store.server may not be set when running in test-suite.
Fix: fs_storage.get_by_id() does not return object if id is integer.

But integer-ids are used all over the place, let alone in the
__main__-part of the module itself. And in the wmc_mapping lambdas.
Fix actions: Not passing headers to the remove-call.

This was buggy since 2009-07-26! Obviously nobody ran
test_content_directory_server since then.
Fix: Pass the user-agent on to the HTTPClient.

This did not work, since the agent-name is in the field `user-agent`,
but need to be passed in `agent`.