"Connection data" is an imprecise and largely incorrect name; these
structures are actually parsed URLs.  Provide a parser that takes a URL
string and produces a URL structure (if it is valid).

Separate the HTTP redirect handling logic from URL parsing, keeping a
`gitno_connection_data_handle_redirect` whose only job is redirect
handling logic and does not parse URLs itself.

Loosen restriction on wildcard "*" refspecs

Since libssh2 doesn't read host configuration from the config file,
this callback can be used to hand over URL resolving to the client
without touching the SSH implementation itself.

When we transform a refspec with a component containing a glob, then
we simply copy over the component until the next separator from
the matching ref. E.g. if we have a ref "refs/heads/foo/bar" and
a refspec "refs/heads/*/bar:refs/remotes/origin/*/bar", we:

1. Copy over everything until hitting the glob from the <dst>
   part: "refs/remotes/origin/".
2. Strip the common prefix of ref and <src> part until the glob,
   which is "refs/heads/". This leaves us with a ref of "foo/bar".
3. Copy from the ref until the next "/" separator, resulting in
   "refs/remotes/origin/foo".
4. Copy over the remaining part of the <dst> spec, which is
   "bar": "refs/remotes/origin/foo/bar".

This worked just fine in a world where globs in refspecs were
restricted such that a globbing component may only contain a
single "*", only. But this restriction has been lifted, so that a
glob component may be nested between other characters, causing
the above algorithm to fail. Most notably the third step, where
we copy until hitting the next "/" separator, might result in a
wrong transformation. Given e.g. a ref "refs/gbranchg/head" and a
refspec "refs/g*g/head:refs/remotes/origin/*", we'd also be
copying the "g" between "branch" and "/" and end up with the
wrong transformed ref "refs/remotes/origin/branchg".

Instead of copying until the next component separator, we should
copy until we hit the pattern after the "*". So in the above
example, we'd copy until hitting the string "g/head".

In commit cd377f45c9 (refs: loosen restriction on wildcard "*"
refspecs, 2015-07-22) in git.git, the restrictions on wildcard
"*" refspecs has been loosened. While wildcards were previously
only allowed if the component is a single "*", this was changed
to also accept other patterns as part of the component.

We never adapted to that change and still reject any wildcard
patterns that aren't a single "*" only. Update our tests to
reflect the upstream change and adjust our own code accordingly.

Update internal usage of `git_transfer_progress` to
`git_indexer_progreses`.

Move to the `git_error` name in the internal API for error-related
functions.

Update internal usage to use the `git_reference` names for constants.