Log Message:
Update to 2.2.1. From the changelog:

* We used to allow committing a path ".Git/config" with Git that is
  running on a case sensitive filesystem, but an attempt to check out
  such a path with Git that runs on a case insensitive filesystem
  would have clobbered ".git/config", which is definitely not what
  the user would have expected.  Git now prevents you from tracking
  a path with ".Git" (in any case combination) as a path component.

* On Windows, certain path components that are different from ".git"
  are mapped to ".git", e.g. "git~1/config" is treated as if \ 
it were
  ".git/config".  HFS+ has a similar issue, where certain unicode
  codepoints are ignored, e.g. ".g\u200cit/config" is treated as if
  it were ".git/config".  Pathnames with these potential issues are
  rejected on the affected systems.  Git on systems that are not
  affected by this issue (e.g. Linux) can also be configured to
  reject them to ensure cross platform interoperability of the hosted
  projects.

* "git fsck" notices a tree object that records such a path that can
  be confused with ".git", and with receive.fsckObjects configuration
  set to true, an attempt to "git push" such a tree object will be
  rejected.  Such a path may not be a problem on some filesystems
  but in order to protect those on HFS+ and on case insensitive
  filesystems, this check is enabled on all platforms.

A big "thanks!" for bringing this issue to us goes to our friends in
the Mercurial land, namely, Matt Mackall and Augie Fackler.

Also contains typofixes, documentation updates and trivial code clean-ups.

Changes since v2.2.0 are as follows:

Hartmut Henkel (1):
      l10n: de.po: fix typos

Jeff King (8):
      unpack-trees: propagate errors adding entries to the index
      read-tree: add tests for confusing paths like ".." and \ 
".git"
      verify_dotfile(): reject .git case-insensitively
      t1450: refactor ".", "..", and ".git" fsck tests
      fsck: notice .git case-insensitively
      utf8: add is_hfs_dotgit() helper
      read-cache: optionally disallow HFS+ .git variants
      fsck: complain about HFS+ ".git" aliases in trees

Johannes Schindelin (3):
      path: add is_ntfs_dotgit() helper
      read-cache: optionally disallow NTFS .git variants
      fsck: complain about NTFS ".git" aliases in trees