Introduce a new `git_path_diriter` that can iterate directories
efficiently for each platform.

Changed win32/path_w32.c to utilize NTFS' FindFirst..FindNext data instead of doing an lstat per file. Avoiding unnecessary directory opens and file scans reduces IO, improving overall performance. Effect is magnified due to NTFS being a kernel mode file system (as opposed to user mode).

Minimizing the number directory and file opens, minimizes the amount of IO thus reducing the overall cost of performing ignore operations.

Fix wrong format string in git_reflog_drop() error message

Validate configuration keys

Use SecureTransport on OS X

On close, we might get a return code which looks like an error but just
means that the other side closed gracefully. Handle that.

Anything SSL is deprecated. Let's make sure we don't try to use SSL v3
when talking to the server.

Do not automatically fail on a bad certificate, but let the caller
decide. This means we don't need our switch on errors anymore but can
return a string representation from the security framework.

This is what it's meant all along, but now we actually have multiple
implementations, it's clearer to use the name of the library.

Instead, provide git_tls_stream_new() to ask for the most appropriate
encrypted stream and use it in our HTTP transport.

As an alternative to OpenSSL when we're on OS X. This one can actually
take advantage of stacking the streams.

config_write -- handle duplicate section headers when deleting entries

Closes #2966.

Fix git_checkout_tree() to do index filemodes correctly on Windows.

Fix for Issue #3023 tests fail with no network

Moved offending tests from network to online so they will get skipped
when there is a lack of network connectivity:
-test_online_remotes__single_branch
-test_online_remotes__restricted_refspecs

Attempt to fix Windows TLS memory leak.

If git_config_delete is to work properly in the presence of duplicate section
headers, it cannot stop searching at the end of the first matching section, as
there may be another matching section later.
When config_write is used for deletion (value = NULL), it may only terminate
when the desired key is found or there are no sections left to parse.

Instead of using a config file in resources, include the config file content to
be tested directly in the test.

Add a unittest to validate bug #3043, where a duplicate empty config header
could cause deletion of a config entry to fail silently. The bug is currently
unresolved and this test will fail.

Rebase fixes

Handle invalid multiline configuration