Log Message:
libgit2: update to 0.27.0.

v0.27
---------

### Changes or improvements

* Improved `p_unlink` in `posix_w32.c` to try and make a file writable
  before sleeping in the retry loop to prevent unnecessary calls to sleep.

* The CMake build infrastructure has been improved to speed up building time.

* A new CMake option "-DUSE_HTTPS=<backend>" makes it possible \ 
to explicitly
  choose an HTTP backend.

* A new CMake option "-DSHA1_BACKEND=<backend>" makes it \ 
possible to explicitly
  choose an SHA1 backend. The collision-detecting backend is now the default.

* A new CMake option "-DUSE_BUNDLED_ZLIB" makes it possible to \ 
explicitly use
  the bundled zlib library.

* A new CMake option "-DENABLE_REPRODUCIBLE_BUILDS" makes it possible to
  generate a reproducible static archive. This requires support from your
  toolchain.

* The minimum required CMake version has been bumped to 2.8.11.

* Writing to a configuration file now preserves the case of the key given by the
  caller for the case-insensitive portions of the key (existing sections are
  used even if they don't match).

* We now support conditional includes in configuration files.

* Fix for handling re-reading of configuration files with includes.

* Fix for reading patches which contain exact renames only.

* Fix for reading patches with whitespace in the compared files' paths.

* We will now fill `FETCH_HEAD` from all passed refspecs instead of overwriting
  with the last one.

* There is a new diff option, `GIT_DIFF_INDENT_HEURISTIC` which activates a
  heuristic which takes into account whitespace and indentation in order to
  produce better diffs when dealing with ambiguous diff hunks.

* Fix for pattern-based ignore rules where files ignored by a rule cannot be
  un-ignored by another rule.

* Sockets opened by libgit2 are now being closed on exec(3) if the platform
  supports it.

* Fix for peeling annotated tags from packed-refs files.

* Fix reading huge loose objects from the object database.

* Fix files not being treated as modified when only the file mode has changed.

* We now explicitly reject adding submodules to the index via
  `git_index_add_frombuffer`.

* Fix handling of `GIT_DIFF_FIND_RENAMES_FROM_REWRITES` raising `SIGABRT` when
  one file has been deleted and another file has been rewritten.

* Fix for WinHTTP not properly handling NTLM and Negotiate challenges.

* When using SSH-based transports, we now repeatedly ask for the passphrase to
  decrypt the private key in case a wrong passphrase is being provided.

* When generating conflict markers, they will now use the same line endings as
  the rest of the file.

### API additions

* The `git_merge_file_options` structure now contains a new setting,
  `marker_size`.  This allows users to set the size of markers that
  delineate the sides of merged files in the output conflict file.
  By default this is 7 (`GIT_MERGE_CONFLICT_MARKER_SIZE`), which
  produces output markers like `<<<<<<<` and \ 
`>>>>>>>`.

* `git_remote_create_detached()` creates a remote that is not associated
  to any repository (and does not apply configuration like 'insteadof' rules).
  This is mostly useful for e.g. emulating `git ls-remote` behavior.

* `git_diff_patchid()` lets you generate patch IDs for diffs.

* `git_status_options` now has an additional field `baseline` to allow creating
  status lists against different trees.

* New family of functions to allow creating notes for a specific notes commit
  instead of for a notes reference.

* New family of functions to allow parsing message trailers. This API is still
  experimental and may change in future releases.

### API removals

### Breaking API changes

* Signatures now distinguish between +0000 and -0000 UTC offsets.

* The certificate check callback in the WinHTTP transport will now receive the
  `message_cb_payload` instead of the `cred_acquire_payload`.

* We are now reading symlinked directories under .git/refs.

* We now refuse creating branches named "HEAD".

* We now refuse reading and writing all-zero object IDs into the
  object database.

* We now read the effective user's configuration file instead of the real user's
  configuration in case libgit2 runs as part of a setuid binary.

* The `git_odb_open_rstream` function and its `readstream` callback in the
  `git_odb_backend` interface have changed their signatures to allow providing
  the object's size and type to the caller.