security/git-crypt: Import git-crypt version 0.7.0 from wip.

git-crypt enables transparent encryption and decryption of files in a
git repository.  Files which you choose to protect are encrypted when
committed, and decrypted when checked out.  git-crypt lets you freely
share a repository containing a mix of public and private content.
git-crypt gracefully degrades, so developers without the secret key can
still clone and commit to a repository with encrypted files.  This lets
you store your secret material (such as keys or passwords) in the same
repository as your code, without requiring you to lock down your entire
repository.

(nikita)