Don't depend on the whole of Vibe.d for the test_registry ...

Makes the code a bit more verbose, but remove the dependency to vibe-d:mongodb,
which happens to be the one currently failing on master.

Update Vibe.d to v0.9.0 in test_registry

test_registry: Parse the port as a ushort, not a uint ...

Otherwise we get a failure inside Vibe.d when the port is > ushort.max,
which can happen easily, e.g. on Mac OSX.

Replace ? with __ for Windows support

Include a special API File Handler that works with query parameters

Bump vibe.d to 0.8.3-alpha.1 for compatibility with dmd-nightly

test fallback mirror usage on server errors

fix retry on http status error ...

- silent http status errors (e.g. 502) should be responsible
  for most "corrupted" zip packages

more robust testing ...

- require arguments for test_registry
- check removal of broken package

Don't break out of the retry loop for ZipExceptions - fixes #1336