Our ssh tests assume that the server supports password authentication
in a few places. This is convenient as we're not testing authentication
methods, but what happens around them.

Tell sshd on OSX to accept this form of authentication.

For urls where we do not specify a username, we must handle the case
where the ssh transport asks us for the username.

Test also that switching username fails.

In order to know which authentication methods are supported/allowed by
the ssh server, we need to send a NONE auth request, which needs a
username associated with it.

Most ssh server implementations do not allow switching the username
between authentication attempts, which means we cannot use a dummy
username and then switch. There are two ways around this.

The first is to use a different connection, which an earlier commit
implements, but this increases how long it takes to get set up, and
without knowing the right username, we cannot guarantee that the
list we get in response is the right one.

The second is what's implemented here: if there is no username specified
in the url, ask for it first. We can then ask for the list of auth
methods and use the user's credentials in the same connection.

Since each cred defines the username on their own, introduce
git_cred__username to retrieve the username pointer from them.

This exists as ssh needs to know about the username to use before it can
query for the supported authentication methods.

Instead of completely giving up on the first failure, ask for
credentials as long as we fail to authenticate.

Introduce this error code to signal an authentication failure.

We need to be able to get a GIT_EUSER back through the outermost call.

Before calling the credentials callback, ask the sever which
authentication methods it supports and report that to the user, instead
of simply reporting everything that the transport supports.

In case of an error, we do fall back to listing all of them.

Add docs for git_clone_local_t and move the docs for the
git_clone_options to each field.

revwalk: more sensible array handling

Instead of using a sentinel empty value to detect the last commit, let's
check for when we get a NULL from popping the stack, which lets us know
when we're done.

The current code causes us to read uninitialized data, although only on
RHEL/CentOS 6 in release mode. This is a readability win overall.

treebuilder: insert sorted

By inserting in the right position, we can keep the vector sorted,
making entry insertion almost twice as fast.

Bump library version to 0.21.0 and SONAME to 21

Since the SOVERSION doesn't need to follow the library's version and
simply needs to be monotonically increasing whenever we release
something that breaks the ABI, we can set some number and allow multiple
versions of the library to be installed side-by-side.

We start here with the minor version as that's what we release for now,
and it allows to backport this change to earlier versions.

More remote rename fixes

Win32: Fix object::cache::threadmania test on x64

Win32 test fixes

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.

Remote rename fixes

Update AUTHORS

Add me. :)

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.

When there is a reference in the target namespace, we should overwrite
it. Instead it gets a different name under the current code.

clone: re-use the local transport's path resolution

Concurrent ref iterator access

Whe already worked out the kinks with the function used in the local
transport. Expose it and make use of it in the local clone method
instead of trying to work it out again.