Merge branch 'ib/t3700-add-chmod-x-updates'

The t3700 test about "add --chmod=-x" have been made a bit more robust and generally cleaned up. * ib/t3700-add-chmod-x-updates: t3700: add a test_mode_in_index helper function t3700: merge two tests into one t3700: remove unwanted leftover files before running new tests