The callback-based method of listing remote references dates back to the
beginning of the network code's lifetime, when we didn't know any
better.
We need to keep the list around for update_tips() after disconnect() so
let's make use of this to simply give the user a pointer to the array so
they can write straightforward code instead of having to go through a
callback.
The text progress and update_tips callbacks are already part of the
struct, which was meant to unify the callback setup, but the download
one was left out.
The subtransport path was relying on pointing to data owned by
the remote which meant that after a redirect, the updated path
was getting lost for future requests. This updates the http
transport to strdup the path and maintain its own lifetime.
This also pulls responsibility for parsing the URL back into the
http transport and isolates the functions that parse and free that
connection data so that they can be reused between the initial
parsing and the redirect parsing.
