Support string concat and concat-head operations

Doctor's orders: !938 (comment 14975)

We should add tests to ensure that this works

added 5 commits

• ed0964a6...bd48a3d3 - 4 commits from branch redox-os:master
• 7d63cd7a - Support string concat and concat-head operations

Compare with previous version

added 1 commit

• 615e4f87 - Add integration tests

Compare with previous version

enabled an automatic merge when the pipeline for 615e4f87 succeeds

merged

mentioned in commit fd237179