Inside `git_remote_load`, the calls to `get_optional_config` use
`giterr_clear` to unset any errors that are set due to missing config
keys. If neither a fetch nor a push url config was found for a remote,
we should set an error again.
The order in this function is the opposite to what
create_with_fetchspec() has, so change this one, as url-then-refspec is
what git does.
As we need to break compilation and the swap doesn't do that, let's take
this opportunity to rename in-memory remotes to anonymous as that's
really what sets them apart.
