This was a bad idea. Don't free except in the free function.

A symref inside the namespace gets renamed, we should make it point to
the target's new name.

This is for the origin/HEAD -> origin/master type of situations.

There is no reason why we need to use a callback here. A string array
fits better with the usage, as this is not an event and we don't need
anything from the user.

We must make sure that the name pointer remains valid, so make sure to
allocate the new one before freeing the old one and swap them so the
user never sees an invalid pointer.

We don't allow renames of anonymous remotes, so there's no need to
handle them.

A remote is always associated with a repository, so there's no need to
check for that.

Tighten up which references we consider for renaming so we don't try to
rename unrelated ones and end up with unexplained references.

If there is a reference on the target namespace, git overwrites it, so
let's do the same.

Remote: Set an error when a remote cannot be found.

When removing the remote-tracking branches, build up the list and remove
in two steps, working around an issue with the iterator. Removing while
we're iterating over the refs can cause us to miss references.

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.

If the remote supports the symref protocol extension, then we return
that, otherwise we guess with git's rules.