Merge branch 'ar/diff-args-osx-precompose' into maint

Many commands normalize command line arguments from NFD to NFC variant of UTF-8 on OSX, but commands in the "diff" family did not, causing "git diff $path" to complain that no such path is known to Git. They have been taught to do the normalization. * ar/diff-args-osx-precompose: diff: run arguments through precompose_argv