Merge branch 'pw/merge-tree-stdin-deadlock-fix'

"git merge-tree --stdin" has been improved (including a workaround
for a deadlock).

* pw/merge-tree-stdin-deadlock-fix:
  merge-tree: fix link formatting in html docs
  merge-tree: improve docs for --stdin
  merge-tree: only use basic merge config
  merge-tree: remove redundant code
  merge-tree --stdin: flush stdout to avoid deadlock

diff --cc Documentation/git-merge-tree.adoc
Simple merge