Merge branch 'dj/log-graph-with-no-walk'

"git log --graph --no-walk A B..." is a otcnflicting request that asks nonsense; no-walk tells us show discrete points in the history, while graph asks to draw connections between these discrete points. Forbid the combination. * dj/log-graph-with-no-walk: revision: forbid combining --graph and --no-walk