Merge branch 'jx/t5411-unique-filenames'

Avoid individual tests in t5411 from getting affected by each other
by forcing them to use separate output files during the test.

* jx/t5411-unique-filenames:
  t5411: refactor check of refs using test_cmp_refs
  t5411: use different out file to prevent overwriting

diff --cc t/t5411/common-functions.sh
Simple merge