Can be observed in bugs/issue1013_either_dependency.sh

Note this comment, which apparently used to be true with darcs2
# The obliterate fails with: patches to commute_to_end does not commutex (1)

It's possible that this is fixed due to this patch by Tommy:

  * fix wrong ../path in failing issue1013 test
    hunk ./bugs/issue1013_either_dependency.sh 36
    -darcs get --to-patch init ../tmp_d2 tmp_d
    +darcs get --to-patch init tmp_d2 tmp_d

I commented out the exit 1 which was hiding the hang and the test failed as
expected (instead of hanging).

Before we close this off, though I'd like to have an explanation of why we were
getting the hang and how the patch fixes it.

I'm retiring this issue and the corresponding tests (which does not fail
with darcs-2 patch semantics) for not being investigated for a long time.