Clean: Move default config-values and other consts to the top.
Cleanup building the wmc_mapping.

I thought, putting this into  loop or using a generator would give
nicer code, but it does not really. So 'm just rearranging the constant
to make it easier to read and understand.
Add a 'fix me' comment.
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`.
Merge branch 'maintain/0.6.x' into develop
Clean up test_content_directory_server so semantics becomes clear.

The prior code's semantics was hard to understand due to the deep code-
nesting, frequently used try-except-clauses and such. Now the code
uses a decorator to wrap the callbacks by try-except and ensure errback()
is called on failure.

There are still quite some redundancies to be removed, e.g. the device
query.

I'm pushing this to branch `maintain/0.6.x`, even if it is a large,
non-bug-fixing change, since it helps building further test-cases so much.
Merge branch 'maintain/0.6.x' into develop