Sync with v2.2.1

* maint:
Git 2.2.1
Git 2.1.4
Git 2.0.5
Git 1.9.5
Git 1.8.5.6
fsck: complain about NTFS ".git" aliases in trees
read-cache: optionally disallow NTFS .git variants
path: add is_ntfs_dotgit() helper
fsck: complain about HFS+ ".git" aliases in trees
read-cache: optionally disallow HFS+ .git variants
utf8: add is_hfs_dotgit() helper
fsck: notice .git case-insensitively
t1450: refactor ".", "..", and ".git" fsck tests
verify_dotfile(): reject .git case-insensitively
read-tree: add tests for confusing paths like ".." and ".git"
unpack-trees: propagate errors adding entries to the index

diff --cc Documentation/config.txt
Simple merge

diff --cc Documentation/git.txt
Simple merge

diff --cc config.c
Simple merge

diff --cc unpack-trees.c
Simple merge