We use `git_error_set_after_callback_function` to determine whether
`update_tips` returned an error but do not store its return value making us
think it always returns 0.

Fix it by adding the common patter of storing it inside the `if` when calling it.

Provide a mechanism for (internal) users to determine a remote's
capabilities from the transport.

Move the functionality to update an individual tip out of the loop;
although the update tip function remains rather gnarly, at least the
outer function is a bit less onerous.

Pull ref updating into its own function for future uses.

Give callers the ability to select how to handle redirects - either
supporting redirects during the initial connection (so that, for
example, `git.example.com/repo` can redirect to `github.com/example/repo`)
or all/no redirects.  This is for compatibility with git.

The existing mechanism for providing options to remote fetch/push calls,
and subsequently to transports, is unsatisfactory.  It requires an
options structure to avoid breaking the API and callback signatures.

1. Introduce `git_remote_connect_options` to satisfy those needs.

2. Add a new remote connection API, `git_remote_connect_ext` that will
   take this new options structure.  Existing `git_remote_connect` calls
   will proxy to that.  `git_remote_fetch` and `git_remote_push` will
   proxy their fetch/push options to that as well.

3. Define the interaction between `git_remote_connect` and fetch/push.
   Connect _may_ be called before fetch/push, but _need not_ be.  The
   semantics of which options would be used for these operations was
   not specified if you specify options for both connect _and_ fetch.
   Now these are defined that the fetch or push options will be used
   _if_ they were specified.  Otherwise, the connect options will be
   used if they were specified.  Otherwise, the library's defaults will
   be used.

4. Update the transports to understand `git_remote_connect_options`.
   This is a breaking change to the systems API.