Merge branch 'xx/diff-tree-remerge-diff-fix'

"git rev-list ... | git diff-tree -p --remerge-diff --stdin" should behave more or less like "git log -p --remerge-diff" but instead it crashed, forgetting to prepare a temporary object store needed. * xx/diff-tree-remerge-diff-fix: diff-tree: fix crash when used with --remerge-diff