Merge branch 'ew/empty-merge-with-dirty-index'

"git merge -s recursive" did not correctly abort when the index is dirty, if the merged tree happened to be the same as the current HEAD, which has been fixed. * ew/empty-merge-with-dirty-index: merge-recursive: avoid incorporating uncommitted changes in a merge move index_has_changes() from builtin/am.c to merge.c for reuse t6044: recursive can silently incorporate dirty changes in a merge