Merge branch 'da/mergetool-tool-help'

Allow "git mergetool --help" to run outside a Git repository.

* da/mergetool-tool-help:
  difftool: don't assume that default sh is sane
  mergetool: don't require a work tree for --tool-help
  git-sh-setup: move GIT_DIR initialization into a function
  mergetool: use more conservative temporary filenames
  test-lib-functions: adjust style to match CodingGuidelines
  t7610-mergetool: prefer test_config over git config

diff --cc git-mergetool.sh
index 96a61ba6f470d7634552a42547de57f63fae8d81,821253e3688ca3fdc9091334984b5125a15abc33..ec644d542d9754fa09ac7fb1b0f1f932a9bedbed
--- 1/git-mergetool.sh
--- 2/git-mergetool.sh
+++ b/git-mergetool.sh
@@@ -378,16 -381,12 +382,19 @@@ prompt_after_failed_merge () 
        done
  }
  
+ git_dir_init
+ require_work_tree
+ 
  if test -z "$merge_tool"
  then
 -      merge_tool=$(get_merge_tool "$merge_tool") || exit
 +      # Check if a merge tool has been configured
 +      merge_tool=$(get_configured_merge_tool)
 +      # Try to guess an appropriate merge tool if no tool has been set.
 +      if test -z "$merge_tool"
 +      then
 +              merge_tool=$(guess_merge_tool) || exit
 +              guessed_merge_tool=true
 +      fi
  fi
  merge_keep_backup="$(git config --bool mergetool.keepBackup || echo true)"
  merge_keep_temporaries="$(git config --bool mergetool.keepTemporaries || echo false)"

diff --cc git-sh-setup.sh
Simple merge