Compose element throws away files inside directory symlinks at integration time

There has been a regression in the compose element in the 1.1 branch.

I have written a testcase which can be found in branch sam/compose-symlinks-issue to demonstrate the issue.

I proposed a fix in !295 (merged), but there is something funky going on as the testcase I added to guard against regressions fails in CI but passes for me locally.