"cred.h" is missing in releas tarball #5343

Reproduction steps

1. Download release tarball https://github.com/libgit2/libgit2/archive/v0.28.4.tar.gz
2. Browse archive and look for "cred.h"

Expected behavior

"cred.h" is part of tarbal, as this is required to build "git2go".

Actual behavior

"cred.h" is missing in release tarball

Version of libgit2 (release number or SHA1)

0.28.4

Operating system(s) tested

Arch Linux (https://git.archlinux.org/svntogit/packages.git/tree/trunk/PKGBUILD?h=packages/libgit2)