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.

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

Documentation formatting fixes

The documentation has shown this as a single enum for a long time. These
should in fact be two enums. One with the bits for the flags and another
with the bits for the extended flags.

These are some issues I found while playing around with the new parser
for docurium.

This lets us work without worrying about what's happening but work on a
snapshot.

If we remove a reference while we're iterating through the packed refs,
the position in the iterator will be off.

remote: build up the list of refs to remove