Merge branch 'ks/tree-diff-walk'

* ks/tree-diff-walk: tree-walk: finally switch over tree descriptors to contain a pre-parsed entry revision: convert to using diff_tree_sha1() line-log: convert to using diff_tree_sha1() tree-diff: convert diff_root_tree_sha1() to just call diff_tree_sha1 with old=NULL tree-diff: allow diff_tree_sha1 to accept NULL sha1