Log unpacking errors during import. Closes #310
Improve error message on missing 'unp' requirement

See #310
Add testcase for a748078b21c9a270b6925e52b6b944bd0f4b4dd3, migrate to Rspec
Introduce "InstallError" (code 0001) and raise that on missing 'unp'

See #310. The error message asks users to notify support about these.
Merge CDB-1517 into release/2.8.2