Allow proxy options when connecting with a detached remote.

merge: Check file mode when resolving renames

Initialise cfg variable.

Co-authored-by: Edward Thomson <ethomson@github.com>

Update README.md

When determining if ours or theirs changed, we check the oids but not
their respective file modes. This can lead to merges introducing incorrect
file mode changes (eg., in a revert). A simple linear example might be:

commit A - introduces file `foo` with chmod 0755
commit B - updates some unrelated file
commit C - renames `foo` to `bar` and chmod 0644

If B is reverted, `bar` will unexpectedly acquire mode 0755.

Discover libssh2 without pkg-config

Co-authored-by: Edward Thomson <ethomson@github.com>

Co-authored-by: Edward Thomson <ethomson@github.com>

Use __typeof__ GNUC keyword for ISO C compatibility

indexer: Avoid one `mmap(2)`/`munmap(2)` pair per `git_indexer_append` call

Support custom git extensions

Fix coding style for pointer

Fix config parsing for multiline with multiple quoted comment chars

notes: use a buffer internally

If longpaths is true and filters are enabled, pass git_repository through the filtering code to ensure the cached longpath setting is returned.

Fixes: #6054

Add git24j to the language bindings

Code cleanup to use `git_buf`s instead of simple c strings.

The strip_comments function uses the count of quotes to know if a
comment char (';' or '#') is the start of a comment or part of the
multiline as a string.
Unfortunately converting the count of quotes from previous lines to a
boolean meant that it would only work as expected in some cases
(0 quotes or an odd number of quotes).

This tests parsing a multiline string containing multiple quoted comment
chars. See #6019

Make some syntax change to follow coding style.

Turns out, double negatives are harder to parse than positive
statements.

It turns out that if we use `mmap(2)`, non-Windows remote filesystems
break due to permissions. If we don't, _Windows_ remote filesystems
break due to lack of coherence between memory mapped views of the file
and direct I/O operations done to the files.

To break out of this impossible situation, conditionally-compile
versions of Windows-specific `write_at` and `append_to_pack`.

Now that we're not using `mmap(2)` for writing stuff, we don't need to
truncate the file afterwards, since it'll have the correct size at the
end of the process. Whee~!

This change makes `append_to_pack` completely rely on `p_pwrite` to do
all its I/O instead of splitting it between `p_pwrite` and a
`mmap(2)`/`munmap(2)`+`memcpy(3)`. This saves a good chunk of user CPU
time and avoids making two syscalls per round, but doesn't really cut
down a lot of wall time (~1% on cloning the
[git](https://github.com/git/git.git) repository).

This change makes `git_remote_name_is_valid` be part of the public
interface of the library. This is needed for other language bindings to
be able to find this symbol (like in git2go, when linking against
libgit2 dynamically).

Allow users to specify additional repository extensions that they want
to support.  For example, callers can specify that they support
`preciousObjects` and then may open repositories that support
`extensions.preciousObjects`.

Similarly, callers may opt out of supporting extensions that the library
itself supports.

#6028: Check if `threadstate->error_t.message` is not `git_buf__initbuf` before freeing.

This follows the same principle as `buffer.c` where the same check is done before freeing the buffer. It fixes the crash described in #6028.