README: be more explicit in the goals and scope

Gift deprecated in favor of SwiftGit2

refdb: bubble up recursive rm when locking a ref

pack: dereference cached pack entry on error

Fix off-by-one problems in git_signature__parse

Make it clearer from the get-go that we do not aim to implement
user-facing commands from the git tool.

Etc/GMT-14 aka UTC+14:00 is a thing....
https://en.wikipedia.org/wiki/UTC%2B14:00

Also allow offsets on the last minute (59).

Addresses: https://bugs.debian.org/841532
Fixes: #3970

rebase: plug a leak in the tests

Failure to bubble up this error means some locking errors do not get reported as
such on Windows.

refdb: disable concurrent compress in the threading tests on Windows

Various fixes

This is far from an ideal situation, but this causes issues on Windows which
make it harder to develop anything, as these tests hit issues which relate
specifically to the Windows filesystem like permission errors for files we
should be able to access. There is an issue likely related to the ordering of
the repack, but there's enough noise that it does not currently help us to run
this aspect of the test in CI.

When trying to uncompress deltas in a packfile's delta chain, we try to
add object bases to the packfile cache, subsequently decrementing its
reference count if it has been added successfully. This may lead to a
mismatched reference count in the case where we exit the loop early due
to an encountered error.

Fix the issue by decrementing the reference count in error cleanup.

The function `cl_git_thread_check()` is defined as static. As the
function is defined in a header file which is included by our
tests, this can result in warnings for every test file where
`cl_git_thread_check` is never used.

Fix the issue by marking it as inline instead.

git_rebase_init: correctly handle detached HEAD

Properly pass `wchar *` type to giterr_set

remote: fix typo in git_fetch_init_options docs

git_rebase_finish relies on head_detached being set, but
rebase_init_merge was only setting it when branch->ref_name was unset.
But branch->ref_name would be set to "HEAD" in the case of detached
HEAD being either implicitly (NULL) or explicitly passed to
git_rebase_init.

Introduce some clar helpers for child threads

Don't `cl_git_pass` in a child thread.  When the assertion fails, clar
will `longjmp` to its error handler, but:

> The effect of a call to longjmp() where initialization of the jmp_buf
> structure was not performed in the calling thread is undefined.

Instead, set up an error context that threads can populate, and the
caller can check.

We want a predictable number of initializations in our multithreaded
init test, but we also want to make sure that we have _actually_
initialized `git_libgit2_init` before calling `git_thread_create` (since
it now has a sanity check that `git_libgit2_init` has been called).

Since `git_thread_create` is internal-only, keep this sanity check.
Flip the invocation so that we `git_libgit2_init` before our thread
tests and `git_libgit2_shutdown` again after.

Introduce `git_thread_exit`, which will allow threads to terminate at an
arbitrary time, returning a `void *`.  On Windows, this means that we
need to store the current `git_thread` in TLS, so that we can set its
`return` value when terminating.

We cannot simply use `ExitThread`, since Win32 returns `DWORD`s from
threads; we return `void *`.

use `giterr_set_str()` wherever possible

`giterr_set()` is used when it is required to format a string, and since
we don't really require it for this case, it is better to stick to
`giterr_set_str()`.

This also suppresses a warning(-Wformat-security) raised by the compiler.

Signed-off-by: Pranit Bauva <pranit.bauva@gmail.com>

Bump version number to v0.25

sortedcache: plug leaked file descriptor