Dynamic inheritance in OptionTrees

[jlstevens]

This PR is primarily to find out whether disabling merge_keywords has an effect on the test. If the tests continue to pass, then I propose keeping it disabled.

Edit: This PR turned into a fix for dynamic inheritance.

[jlstevens]

Thanks for that last fix! Hope the tests pass this time...

[jlstevens]

The existing tests passed and I am currently adding more unit tests. I should also mention that there is no need to change merge_keywordsand that this PR addresses issue #646.

[jlstevens]

I looked into the possibility of defining a utility to replace this code for generating a string specification:

components = (obj.__class__.__name__,
                        group_sanitizer(obj.group),
                        label_sanitizer(obj.label))
 '.'.join([c for c in components if c])

But decided this pattern doesn't appear often enough in the codebase to bother with after grepping for '.'.join(. For tuple specifications, there is already get_spec(obj) which seems sufficient as tuple specs are recommended anyway.

Having added unit tests to ensure the new dynamic inheritance keeps working, I think this PR is now ready for a review/merge.

[jlstevens]

I added one more unit test to simulate the %%opts magic. Ready to review/merge.

[jlstevens]

I just updated the title of the PR as I confused myself thinking it is about options on DynamicMapinstead of dynamic inheritance!

[philippjfr]

Thanks for adding the tests. Very happy we finally fixed this.