Merge branch 'lt/decorate'

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