If .done() is _not_ used, we trigger another upload to the server - not
clear if this is the best behavior.

With .done(), we simply return the same metadata with a 204 which we
returned with the last PATCH.

Unfortunately, I was not able to exactly reproduce the bug as
documented, but I am confident that this should fix it.

Fixes #1 (I hope)

Until now, we used the lnt file from varnish-cache, which suppressed
some errors which are actually interesting for us (e.g. the wrong
VSPLAY_FOREACH() was spotted by flexelint with stricter rules).

we removed an item from the tree while iterating it.

Spotted by flexelint with stricter rules, see follow up commits.

See tree(3bsd)

to be able to do this and see the right object, we need to change the
test case to a private upload directory (defaults to per-vtc working
directory)

to be able to use Lck_AssertHeld()

as of efa1e7d64f8b1a17a02a9fd30df606804ba40a3b