And fixed a bug found by these tests; retrieveKeyFile would fail
when the dest file was already complete.
This commit was sponsored by Bradley Unterrheiner.
This only performs some basic tests so far; no testing of chunking or
resuming. Also, the existing encryption type of the remote is used; it
would be good later to derive an encrypted and a non-encrypted version of
the remote and test them both.
This commit was sponsored by Joseph Liu.
