Merge branch 'ps/shift-root-in-graph' into next

Merge branch 'ps/shift-root-in-graph' into next

'git log --graph' has been modified to visually distinguish parentless
'root' commits (and commits that become roots due to history
simplification) by indenting them, preventing them from appearing
falsely related to unrelated commits rendered immediately above them.

* ps/shift-root-in-graph:
  graph: add --[no-]graph-indent and log.graphIndent
  graph: move config reading into graph_read_config()
  graph: wrap cascading commits after 4 columns
  graph: indent visual root in graph
  graph: add a 2 commit buffer for lookahead
  revision: add next_commit_to_show()
  lib-log-graph: move check_graph function