Merge branch 'jk/4gb-idx'

The code was not prepared to deal with pack .idx file that is larger than 4GB. * jk/4gb-idx: packfile: detect overflow in .idx file size checks block-sha1: take a size_t length parameter fsck: correctly compute checksums on idx files larger than 4GB use size_t to store pack .idx byte offsets compute pack .idx byte offsets using size_t