Return a new reference when iterating over a collection.

[jesper-friis]

Description

Return a new reference when iterating over a collection and ensure that it is decreased again when the instances goes out of scope (memory managed by dlite).

Type of change

• Bug fix & code cleanup
• New feature
• Documentation update
• Test update

Checklist for the reviewer

This checklist should be used as a help for the reviewer.

• Is the change limited to one issue?
• Does this PR close the issue?
• Is the code easy to read and understand?
• Do all new feature have an accompanying new test?
• Has the documentation been updated as necessary?

[francescalb]

Nicely done. However, I think that explaining somewher the reason for this is quite important. I suggest a clarifiying docstring at the top of the test.

[jesper-friis]

Nicely done. However, I think that explaining somewher the reason for this is quite important. I suggest a clarifiying docstring at the top of the test.

done