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

diff --cc Documentation/rev-list-options.txt
Simple merge

diff --cc builtin-log.c
Simple merge