Merge branch 'sg/diff-multiple-identical-renames'

"git diff -M" used to work better when two originally identical
files A and B got renamed to X/A and X/B by pairing A to X/A and B
to X/B, but this was broken in the 2.0 timeframe.

* sg/diff-multiple-identical-renames:
  diffcore: fix iteration order of identical files during rename detection

diff --cc diffcore-rename.c
Simple merge

diff --cc t/t4001-diff-rename.sh
Simple merge