Merge branch 'ah/log-no-graph'

Merge branch 'ah/log-no-graph'

"git log --graph --graph" used to leak a graph structure, and there
was no way to countermand "--graph" that appear earlier on the
command line.  A "--no-graph" option has been added and resource
leakage has been plugged.

* ah/log-no-graph:
  log: add a --no-graph option
  log: fix memory leak if --graph is passed multiple times