Merge branch 'lt/decorate'

* lt/decorate: rev-list documentation: clarify the two parts of history simplification Document "git log --simplify-by-decoration" Document "git log --source" revision traversal: '--simplify-by-decoration' Make '--decorate' set an explicit 'show_decorations' flag revision: make tree comparison functions take commits rather than trees Add a 'source' decorator for commits Conflicts: Documentation/rev-list-options.txt